I imagine it would look odd for a guy to roll out an M1 Garand, 1911, and a pump-action shotgun I'd have to borrow...
Do it and stand proud.
I shot a two gun match with a M1 Carbine & 1911A1. I didn't win, but I was respectable, and I had fun.
I shoot ICORE with a as issued Model 64 and my old HOYT holster I carried in LE. Except for loading (no moon clips) it shot as good as any.
I even shot ICORE with my 642 pocket revolver, drawing from my pants pocket. Couldn't compete with the fancy revolvers and moon clips but I learned a bit more about my SD carry revolver.
I've shot steel matches with my 870, it shoots and is reliable, but of course these are timed matches and I couldn't compete with some guy with a drum mag on his FN shotgun. I also has no jams, couldn't say that for most of the fancy shotguns out there.
Consider you are shooting against yourself, beating your last match's scores.
I'm kind of moving away from high power and more to the CMP GSM Vintage Military Rifle, shooting as issue Garands, Carbine's and Mosins.
Remember the main purpose of these shooting games is to have fun, I have more fun shooting these old pieces of history.