may be awkward though. I’m thinking the numeric keypad (hold for continuous increment/decrement):
7=left track increase speed, 9=right track increase speed, 1=left track decrease speed (or increase speed reverse), 3=right track decrease speed. 8=turret up, 2=turret down, 4=turret rotate left, 6=turret rotate right, and 5=center all (smoothly make tracks nonmoving, rotate turret to neutral, straight ahead position). Could have things like keypad + is increase rate (so, say, holding 7 accelerates the left track more), - is decrease rate, and 0 is reset rate to default.
Other than that, I would personally prefer the Unreal Tournament 3 Goliath tank fly-by-wire controls, mouse for turret and wasd for tank turning and wasd for tank turning and accelerate forward/back. Letting go of the w or s key smoothly decelerates to a stop.