Texas Multigun has a WW2 Division.
Garand, 12 gauge pump, single stack 1911 in 45. WW2 was fun but I am back to 223, semi-auto 12 gauge, and wide-body pistol. The match is adding Vietnam divisions - Light and Heavy, Heavy being M1a/M14, single stack, 12 gauge pump.
Regardless, go out and shoot. As long as you have the minimum caliber, you are ok. Mins are usually 9mm, 223, 20 gauge, but matches vary. A 308 division is usually 308/45/12 gauge, but you can always shoot against the mouse guns if you don't meet Heavy minimums.