ORIGINAL: modelbob71
The M4A1 with large hatch (Mato hull) was not fitted with the 75mm gun, only the 76 mm. The M4A3 had both 75mm , 76 mm and 105 mm guns. See Hunnicutt's book.
Oh, 75mm gun turrets on big hatched A1 hulls? [X(]
Just a few of those were built and most went to conversions as the Duplex Drive tanks.
As a matter of fact, I believe ALL of those large hatched M4A1 75MM Shermans were used as DD tanks. That's why you don't see too many of them around. But I do have a photo or two around at home. When I get the time I'll look around for it/them.
~ Jeff