Most of the Tanks/armored vehicles were used for training and reserve forces. Very limited number being used in actual combat.
Don't know how exactly could you make Land Lease faction, most of land lease equipment is already in default Soviet tier buildings. (most of the trucks, Katyusha truck for example, etc)
Other than that I like your idea
I did a lend lease doctrine a while ago, it was very different to what we actually got:
http://www.coh2.org/topic/12396/new-doctrine--lend-lease