Pretty much. The 105mm turrets are close to a high bustle 75mm, but have the extra turret ventilator tower at the rear, and the mantlet is different and protrudes further from the front of the turret face - I had to take the dremel to both the HL and Tamiya turrets, so that Nicks mantlet sat closer to the turret face (as well as whip off the offending ventilator).

If you are thinking of doing a 75mm turret, the only chassis it would go on currently is the HL M4A3 - there were no 75mm versions of Tamiyas big hatch M4 or Mato's M4A1 (dicounting DD versions anyway).

If you want to do something different, I'd suggest looking at the small hatch M4 - a change of engine deck would make an M4A2 for lend lease service (or USMC), and for the adventurous, a hull stretch makes an M4A4...