Tim Fraizer and I banged bars in the 125 B back in 1982-Nice guy. I rode a friend's 84 RM125 at a few races, you are correct, great suspension and zero low-mid power.
It’s a 78, he had it list as a 79 during Christmas. I got the frame number/a better picture and confirmed it was a 78. He painted the swing arm black so it hard to tell.