You could get away with having his front diagonal and side frames being mirrored, if you don't wanna draw all angles, you could still do that by having your lumps set up like this
E102A1
E102A2A8
E102A3A7
E102A4
E102A5
E102A6
According to the Wiki, anyway.
Sonic Battle Gamma isn't the real Gamma. It's Chaos Gamma, a remake of Gamma, since Gamma is supposed to be dead after Sonic Adventure.
Also, note how Gamma in Sonic Battle has a simpler design than he does in Sonic Adventure. This is because Sonic Battle mirrored the sprites, so he had to be designed symetrically, and he couldn't have his number on him since the grey guard robots also used the same sprites, but palleteswapped.
SRB2 is too low-res to have Gamma's number on him, and there's also the pallete swap issue, but you could still have the gun and, if you choose to do the front frames, his headlamp.