Identifying an "80's preban upper"

[Haskinsjj]

Purchased an upper recently that I was told was an 80's pre ban upper and am attempting to find out as much info on it as possible. Doesn't hurt my feelings if it isn't exactly what the guy said it was, he was easy to deal with.
Emco/Kaiser A2 upper, maybe Bushmaster? Has A2 sight but has A1 tear drop forward assist:
semi-auto bolt carrier, no markings:

Light staking to gas key:

MPC bolt, maybe Colt?

Fibers from a2 round style handguard:

Arrow only on FSB, no "UP":
"J" stamped into FSB:
Diemaco styized "D" barrel:
Old A2 type "crush washer":


It seems like it's just a conglomeration of parts, and could just be a bubba build. No other markings found without completely disassembling the upper. I was happy to have an A2 carry handle upper and the Diemaco barrel if nothing else. Just wondering if anyone has insight as to who may have offered something like this commercially, if anything is norm or out of norm, and opinions. I know, it's got some rust lol gotta clean her up! Planning on doing either a Canadian C7 style build or C7A2 with it. Bore is nice and clean, no outrageous amount of wear on it other than it was in dire need of carbon removal.
Thanks!
J

P.S. I did find cuts on the bolt at a 45 degree angle, looks like this image I found at another forum

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[Mygrainman]

Very cool.. I'm gunna have to follow and learn something here.
If our resident "experts" come up empty, I've had some success IDing things over on the arfcomretro forum..
I've only recently got the retro bug, and am sponging up all the knowledge I can on the subject.

Is that an A2 flash hider, or a bird cage? Can't tell from that angle.

 

[Haskinsjj]

It's an A2 flash hider, no slots on the bottom. Its kinda weird that it's got everything A2 but has a tear drop forward assist. That's what makes me wonder if someone didn't just slap it together. This is my first 'retro-ish' or I suppose classic type rifle. As of right now it's sitting on a regular ol' Anderson lower with a new production A2 stock and new A2 grip. would be neat to find a CS marked A1 stock to put on it.

 

[Old salt]

Interesting

 

[Unka-Boo]

I'm leaning towards "assembled parts"...but, Ye olde Bushmaster must have had a warehouse full of teardrop forward assists because darn near everyone I saw in the '90s had one ( including two I owned )...but they did produce their own barrels back then, would be marked "BMP".