The model should basically be this:
M4A3 Chassis and hull with the 76mm Sherman turret and 75mm gun in it, the additional armor could be skipped because while nice it would require more model work and they would barely be noticeable anyhow.
Sadly the mod tools are severely limited in the modeling department.
Or use the Easy 8 and it's DONE.
Do we need the 75mm barrel ? Barrels hardly reflect performances ANYWAY, look at Churchill which is supposed to have the same gun as Cromwell.
Look how USF 75mm has better pen than Panzer 4 kwk40 despite having slighly more than half the penetration.
M4A3E2 76 (w)
Voila, done, no bs convoluted upgrades.