AFAIK, just use the simple circle-and-pipper sight for any of the early-war US planes, they didnt get too fancy until later on. I don't know how accurately restored it is, but in the Roaring Glory video Jeff Ethell did with Bill Anderson's P-40 at Geneseo years ago, the gunsight is just a simple one.
PM me your e-mail and I'll send you my P-40 sounds, I've mixed and matched and compared with the sounds from that video (I'd record directly from it if I knew how to take audio out) and they match up pretty good.