Modernizing an M3 (M5A1) Stuart in the T2k setting.

[raketenjagdpanzer]

Instead of the Bushmaster Cannon why not

two LAU-68D/A 7-tubes rocket pods with Hydra 70 rockets

or

GAU-8/A Avenger 30mm Cannon

For suppression, the rockets would definitely work well; esp. if loaded with less-than-lethal (smoke, CS) rounds for using against angry civilians whom you'd prefer not to kill in droves.

The GAU-8 is heavy; maybe a -7 or -4