It is not a T-6 or T-6 variant. This is a P-64 which was made by North American so it has some similar looks, but a completely different plane.

The "combat" versions were actually gunnery trainers and were in fact SNJ, Harvard, & T-6 (B) models with various armament setups consisting of a fixed, syncronized 30 cal. on the top of the cowling, another fixed 30 cal. on the inboard leading edge of the right wing (some can be found on the left), and one removable, rear facing, aim-able 30 cal. that could be operated by the backseater by swiveling the rear seat aft.

They were primarily used for gunnery training, but some did in fact see combat.

Most of the "combat versions" have the rear gun removed today in the interest of weight and space, but you will occasionally find one at the airshows with the modified rear canopy and the aft gun still in place.