720/745 knowledge required to resurrect family gun

My grandfather used a Belknap B-65 (a store brand Savage 745) for decades before it was knocked off a vehicle roof and the receiver was broken at the upper tang. An attempt was made to repair the damage but it was a rough job at best. The shotgun was no longer remotely safe to operate having developed a habit of firing when bumped hard, but it soldiered on for a before being eventually being replaced by a Remington 1100.

The shotgun has been dormant for the last 30 years, until I happened to see an ad for A5 receivers. This caused me to do a little research to see if maybe that might work. Of course, this proved to be incompatible, but lead me to find that I could buy a whole working shotgun to use for parts for less than $200.

On that bombshell, all I need to do is find the right Savage, Springfield, Revelation, etc. and get to work. I would seem to be easy, but it isn't so clear cut.

Do the steel framed 720 parts fully interchange with the aluminum 745? What are the differences between the the 745 and 745B or 745C? How might they effect my choice in a donor gun? Does it really matter if I take parts form an gun with sentimental attachment and put them in a new recover? If it seems to in my mind, am I crazy?

Judging by what Numrichs has listed for parts numbers I'd say it was fine to use either of the receivers, the parts numbers from both the 720 and 745's on Numrichs are matched.

For miscellaneous parts you might want to do a search on eBay. I'd also check Gunbroker because I have seen receivers listed. Numrich Arms/Gun Parts Corp has lots of treasure so it might not be a bad idea to contact them.

Numrich arms has a pretty good listing of parts, although most are sold out these days, but the listings would give an pretty good idea of what parts cross over, as posted.