The only difference between the tanks are speed and health.
T-34->KV-1 is a nice idea.How about KV-2->KV-8 flamethrower tank?Only 45mm gun (like a T-70). Churchill Croc is used very rerelly so it will be quite original.
They are called reward units. You can choose to swap them with other units. Please read my post next time.
KV1 has the same gun as a T34, so logically you sacrifice mobility for more armour while keeping the same gun. So in game/balance terms if it were to be a reward unit it would replace the T34/76However that would come with its own problems as the T34 is meant to be upgraded to a T34/85. In turn that menas we'd have to make a second tank KV85...2 tanks for 1 reward unit...ahem...a bit much