RE: SU-100 Gun
Nice thing about Russian tanks, on most vehicles they used almost any style of wheel. So the stock T34/85 wheels would be one type used on the SU-100. Also, using the stock T34/85 barrel is okay, but lenghtening it to resemble the feared L/54 naval gun would be more correct for the SU-100.
With the stock barrel it looks more like a SU-85M.
Jeff