Bundling M42 with stuff isn't going to make the M42 itself any better.
Give it an AoE (like a weaker T-70 gun) or a canister shot ability and the ability to retreat would be quite interesting.
Alternatively, keep the AT role and give it a de-track vehicle ability.
That de-track ability sounds great, though if you mean a total dead-stop, then it could have the same problems as the old Target Weak Point or even the Treadbreak ability of Light AT HT from vCoH.
I'd like to see an ability that cranks up the fire rate up to 11. For example, 30 munitions to have reload time halved for 10 or 15 seconds. If only one in three of your shots penetrate a Panzer IV, then you better fire A LOT of these shots in a short time.