The trouble with any counterbalance to the latest Mark IV's gun is that it was already destroying the front suspension (stripped tyres leading to steel wheels, turret ring strain, etc.) if you add more weight then the entire drivetrain becomes overstressed rather than just the front.
The late IV was not in any position to carry any more weight, she was maxed out.

I also couldn't call a new sloped hull, different suspension, new turret etc. a minor modification. These are not things that can be achieved in the field.

Cheers,
Adam.

__________________
It's only the Internet.