Excellent work. I really like the contrast between the "plain" T-55 and the rusty ass on armor. It really shows the modifications done to the tank nicely, but your work on the base T-55 helps tie it together so it is not too stark a contrast...for example, the turret hatch tops and the top of the main gun.

If I was to make one criticism, constructive of course , it would be that the tracks seem out of place, being so dark and unremarkable. With all the other rust permeating the build, I think rusty tracks would work well. My 2c anyhow.

Again, well done.