Actually the T-34 design changed over the years, primarily with turret design. 1940 turret was rolled and welded steel. The 41/42 turret was cast steel with approximately the same shape and profile as the 1940 turret. The 42/43 turrets were cast steel slightly higher and with a little more room the 41 turret. The late 42/43 turret had a commanders coupla added to the turret roof. From mid 43 on, the turret was enlarged to carry a 3 man crew and the 85 mm gun. The turret race for the 85mm gun turret was the same size as the 76mm turret, so a lot of the earlier 76mm gun T-34s were re-turreted with 85mm gun design. While the turrets and guns were changed often, the automotives remained pretty much the same with the same 500 hp diesel engine as the 1940 version used throughout the war.
Bull Snipe, the last time I got a dissertation like that was from a fellow war gamer who tried to explain to me the differences between the various models of the B-17. Well done. And I agree, for its time the T-34 was the best main battle tank of WW2.