M-4A1 was the gunner's periscope with adjustable reticle on the right side..by scope to put in, is the gun sight missing?. That's going to be hard to find. The standard persiscope was the M-6 and carried thru the M-46. Great deal on prices....when you get your Sherman finished, you'll be all set. Does your 75mm scope have the range reticle in the center or going up the left side? In the center was better as you could adjust the second round easier. Nice thing about M-41-26/46 there wasn't much diff in the gunners telescopes and they could be swapped out if they took a round and they were secondary sights anyway.. Not familiar with the M-39A2. From the high number probably a mid 50s-late 60s.