Yep, that "crouch" might be very handy.
First off, even on a stout vehicle mount, the .50 has a certain "chug" in the recoil impulse delevered back to the shooter. It's near reflex to lean into that a tad. So that AA gunner crouch could be "rotated" foraward a bit and be excellent posing.
Secondly, modeling AM really helps, since that figure already is wearing leggings, if memory serves (might need a '41 field jacket for ETO, though). But, that would be much less work than the conversion to armor crewman.
Next step would be in resolving the big giant debate over whether 3rd actually wore their Numeral Five (what is looks like to an old salt like me) logo on their steel pots into battle (a point of no small contentions among the ETO reenactor community).