MR used '77 CR frame with modified rear loop ; mostly M1 & M2 Elsinore wheels and stuff ; big tank, big seat ; MT up pipe with longer neck ; minimal headlight/ taillight ;no oil injection; 175 had its own rod, barrel and stud pattern - not interchangeable. Very light, reasonable quick but very small, low bike.
Mines in a '77 CR frame, XR 500 twin leading shoe front wheel, CR forks and swingarm, modified CR seat (to fit big tank )... makes it just tall enough for me to ride.....6'4"
Roger