Doc,
Niiice build. I did that one a couple of years ago when I got back into modelling, but it doesn’t come close to your build. Did you use the powders for all the weathering, or just the wheels? Did you do the chipping/weathering with paints and washes?
One comment on the painted vs. unpainted breech blocks. I’d imagine that the direct fire AT weapons in the front lines would have them painted to keep any reflections to a minimum, to keep the gun/crew from being spotted and killed. Probably not as important for indirect fire weapons, or even the guns inside a tank.
Jeff