The barrel is bushmaster but I don't see any forge marking on the upper receiver.
yap. did bushmaster ever used an upper receiver without any forged markings?
I forget when Bushmaster started using black aluminum heat shields (maybe 2003-2004?), but before the switch, they used the same color and type in your pictures (holes in the heat shields matched holes in the polymer handguard).
Also, Bushmaster applies a dry film lube to the interior of the upper. On BCM uppers this film appears almost tan and splotchy - on Bushmaster uppers it appears dull gray and almost always perfectly uniform.
Bushy upper. The bolt carrier has worn away some DFL to reveal the black anodizing underneath. Also circled is where a little DFL spilled over onto black anodizing. Sorry for the flash washing out the contrast