I am pretty sure you cannot install that upper on a new lower. That upper is the ar10B, and the curved place where they meet near the buffer tube is different. I have a B and have not held an A, but was told by Armalite I could not do that. Google "ar10a vs ar10b" and there is a photo showing...
looking for an iron pig ..., prefer late 75 and newer. 2f, 4speed, etc
I would consider an older one for the right price.
or a 6x series, heck I might consider a 7x for the right price, but I really do not fit in those..
I check craigslist, every yard I see with more than 3 cars, behind almost all gas stations and repair shops (many ppl get them, damage or blow the head gasket and do not want the cost of repair... so they sit) and facebook marketplace... though FB is kinda sketchy.. I just sold a 93 with 1fz...
Technically, you can go turkey hunting and be carrying a sidearm...ya know for personal protection, and shoot a hog with that as needed, protecting yourself..