Actually, the receiver "cover" is the serial numbered component, not the nylon "frame". I think that a common Nylon 66 "frame" could be modified to work on a Nylon 76. That said, all of the Nylon series rifles are a PITA to work on. I have had a couple of Nylon 76 rifles and none of them worked particularly well. I found that odd, as the typical Nylon 66 will function and fire reliably, even if it is a rusty barn gun.
Jeff
