Something along this line.
-Crews can now cloak the gun with 25% reduced speed.
-Can retreat.
-Gains 100% increase to penetration when firing its first shot from camouflage with 25% increased accuracy.
-Cost from 200 to 240.
-Can now be suppressed.
-Penetration from 100/80/60 to 110/90/75
Would be fine with me.
The idea of a light AT gun that deals only with light vehicles is hard to make interesting because how is it going to scale? I would also suggest giving the gun a light AI role, as these guns were deadly when loaded with the correct round against infantry.