New to bullseye and I have a question. Can a Marvel Unit 1 by any chance will fit an RIA match .45 ACP frame? I am considering of getting one. And if it will not fit what could be the reason.
In my opinion, just about any mil spec frame will do. The problem you will have is with the internal parts of a cheap gun. It will be expremely likely that you will have loads of trouble setting a reasonable trigger weight and getting it to hold that weight consistently with a cheap hammer, trigger and sear.
I have two of the original Marvel units which would correspond to the current Marvel Unit#1. They fit all of my 465 ACP frames ad an STI Trojan kin 40S&W but do not fit my 9mm 1911's. I opted for an old 1911 military frame and put in some quality innards lightened to a slightly oer 2lb trigger.