Putting aside all of the other evidence against the Book, would it have bern possible for them to misidentify it as the scroll JS translated from?

Not when you factor in the facsimile and the GAEL.

When a defense lawyer has a clearly guilty client he has to
make up fanciful scenarios, out of thin air, to explain all the
clear and convincing evidence that points at his client. If he
can get the jury to assume these are possible, he can get them
to think it's "reasonable doubt" rather than "unreasonable pipe
dreams."

Mormon apologetics works the same way. If they can find some
fanciful way that JS is still a prophet and not pulling the
wool over our eyes then they've created the "reasonable doubt"
regarding the clear and convincing evidence that he was a fake.

The best argument against the "reverse engineering" theory is
that the evidence used for it has been outright lies. They
make a big thing about the "fact" that the marginal hieroglyphs
were added later. To establish this they point out that:

(1) the hieroglyphs are in a different color ink than the
English

and

(2) the hieroglyphs often go over the margin and overwrite the
English, showing that it was added later, as an afterthought
and not at the time of "translation."

Both of these statements are false. Now that the JS papers are
online anyone can see for themselves that they are false.

When poor copies were shown of the manuscripts the hieroglyphs
looked darker than the English. This is because they were
carefully drawn and more ink soaked into the paper. In parts
of the hieroglyphs that were thin lines and not "filled in" it
is the same color as the thin liens of the English.

The second lie is just a bold-faced lie. In fact that the
Egyptian was put down first is clear. In the first place there
is a margin along the left edge. Back then paper was expensive
and one wrote starting at the left edge to the right edge.
That's how the BOM manuscripts look, etc. So this wasn't an
English translation that the "scribes" decided to add some
hieroglyphs to, this was started as a "translation." Also in
various places where the hieroglyphs are too big to fit in the
margin and spill over across the line the English is INDENTED
to accomodate this, which proves that the glyphs were put first
and then the English "translation."

And if that's not enough there's the "Egyptian Alphabet and
Grammar" (EAG) that JS mentions working on in his diary. Part
of the EAG is in Joseph Smith's handwriting, proving that he
was involved in it. The EAG give meaning associated with
various hieroglyphs (not ones recognized by real Egyptologists,
of course) that match the translations of them on the
translation manuscripts in question.

So, no, the "scribes did it" theory doesn't hold water. The
fact that they have to lie to give it traction proves that.

Once the actual photographs of the papyri were published in 1968 and I could clearly see what the Egyptologists pointed out in 1912 as three major mistakes in facsimile #1 were all missing from the original I knew beyond question that the church was a farce and left soon after.

These major mistakes were the human head rather than jackal head on Anubis, the bird head on the ba of the deceased, and the knife in Anubis hand.

In addition to the points Baura cited, the text of the Book of Abraham itself identifies which papyrus fragment it came from:

1:12 "And it came to pass that the priests laid violence upon me, that they might slay me also, as they did those virgins upon this altar; and that you may have a knowledge of this altar, I will refer you to the representation at the commencement of this record."

1:13 "It was made after the form of a bedstead, such as was had among the Chaldeans, and it stood before the gods of Elkenah, Libnah, Mahmackrah, Korash, and also a god like unto that of Pharaoh, king of Egypt."

Since Joseph Smith "identified" certain figures on the facsimile as the gods listed above---and the "Abraham" character refers the reader to "the representation at the beginning of ***THIS RECORD***"---then "this record" (meaning the BOA text) has to refer to the facsimile which features the altar scene.

Also, Joseph Smith's own journal entries make it clear which papyrus fragments he asserted contained the BOA text. Smith had a follower, Reuben Hedlock, make woodcut copies of the facsimiles for publication in Smith's newspaper, the "Times and Seasons":

23 February 1842:
gave Reuben Hedlock instructions concerning the cut for the altar & Gods in
the
RECORDS OF ABRAHAM. as designed for the Times and Seasons.

24 February 1842:
was explaining the RECORDS OF ABRAHAM to the recorder.

1 March 1842:
Correcting the first plate or cut of the RECORDS OF FATHER ABRAHAM prepared by
Reuben Hedlock for the Times and Seasons

2 March 1842:
Read the Proof of the "Times and Seasons" as Editor for the first time, No.
9-Vol 3d in which is the commencement of the BOOK OF ABRAHAM.

4 March 1842:
Exhibiting the BOOK OF ABRAHAM in the ORIGINAL, to Bro. Reuben Hedlock, so
that
he might take the size of the several plates or cuts. and prepare the blocks
for the Times and Seasons. & also gave instruction concerning the arrangement
of the WRITING on the large cut. illustrating the PRINCIPLES OF ASTRONOMY.

8 March 1842:
Commenced Translating from the BOOK OF ABRAHAM, for the 10 No. of the Times &
Seasons

9 March 1842:
continued the TRANSLATION of the BOOK OF ABRAHAM

End quotes. Obviously, the facsimiles which Smith had Hedlock make, and which were published in the "Times and Seasons", are the same facsimiles which are still published as part of the BOA to this day. It doesn't make sense for the "real" BOA source to be on some "missing scroll" as the Mormon apologists assert; every item of evidence which I've detailed here make it absolutely clear that Joseph Smith wanted the world to believe that the scroll which contained the original BOA story was the facsimile which he had copied and published along *with* the BOA story.

One more thing that makes such a claim impossible is the "Egyptian grammar" that JS wrote in his process of "translating" the egyptian papyri. It outlines pretty specifically which egyptian characters are "translated" into what words and sentences in the BoA. His inability to translate egyptian can be verified on a letter by letter basis. Pretending it was another scroll won't save mormonism.

One of Joseph's major mistakes is that he produced whole paragraphs of "translated" material from each hieroglyph. Actually, each character or small group of characters is more like a single English word. Joseph Smith clearly didn't have the slightest clue of what the hell he thought he was doing.

JS figured out that if you lie with great confidence, you can often get away with nearly anything for a while. For him, the length of time that comprised "a while" was defined by those pesky bullet holes in his body.

Karma's a bitch, as they say.

Actually, Joseph Smith re-invented himself four times: New York, Ohio, Missouri, and lastly Illinois. Each time he "got out of dodge" just in time and left behind scores of dis-enchanted followers in each place. Had he not been shot, he would have re-invented himself a fifth time in his planned move to the "State of Deseret".