I must say that I think that the self-propelled 120mm artillery piece would add a bit to the game.
Totally slow and vulnerable, but adding the bombardment factor, and also giving the M8 something to do.
About that M-36, I am clueless. No idea.
The Brits did some cute things to the Sherman, 75mm HV gun and some other modifications. It never had the durability to match the German tanks though (Our Panzer included), and it had a high profile as well.
T-34 was faster, more durable, and had a more effective weapon for most of the war.
For late war scenarios on the western front, the Sherman is a must.
For mid to late war on the eastern front the T-34 is an absolute must.
For early war in the desert, or even Europe, we need the Mathilda and some model of the early Panzer.