Toad, it does not have to be a Mamiya (lens or body). There were tons of M42 screw (aka Universal) mount SLRs and lenses made. There are exceptions as to ALL M42 lenses fitting ALL M42 bodies, but with the number that were manufactured, I would not worry with finding one.
A Pentax Spotmatic will be my first choice (NOT too heavily used: look closely at the wear on the curtain and listen to the shutter speeds, and watch rear curtain opening when body pointed at a bright light at the speed 1/500 or 1/1000). But the Fuji ST series is just as good. And, yes, there were tons of Mamiya DTLs made. They are well constructed, if a bit cumbersome.
SOME M42 lenses simply will not fit fully on ALL M42 SLR bodies. The Mamiya I think might be one, as there is a tiny stationary pin on the rear. But MOST M42 lenses can be 'married' of MOST M42 bodies. - David Lyga