Just a thumbnail reply:
1. Book of Breathings in Egyptology is very commonly copied as the introductory mummification text. Unique features displayed are very important. The knife (why display a knife?), the arms pointing heaven, one hawk (usually two), and the lion couch conveys a unique story different from a typical Book of Breathings illustration.
2. In 1998, The lion couch scene was dicovered up in the ‘Testament of Abraham’ vignette. So when we discover the only other lion couch scene from antiquity, it also refers to Abraham.
3. Jewish Redactor theory. There have a few texts where semitic authors have used Egyptology (i.e., the Egyptian symbol of Hor to represent God) to convey Jewish theology. See above for the references.
4. In all accounts, the total length of all the scrolls comined was nearly 35 feet. The fragments that we have in possession are only about 4 feet in length in total.
5. Egyptian text/scroll are historically tack-ons. Egyptians have been shown to add to the scrolls from various sources and from various cultures. They do not filter out stories but add them to their stories.
6. And finally, the translated English text contains numerous historical evidences (see above) which were not known in Joseph Smith’s day but have proven amazingly accurrate.