Actually there were 3 Factory Experimental classes, A/FX, B/FX and C/FX. Which class you ran in was determined by weight to cubic inches. The A/FX classes were the fastest because they got to carry less weight per c.i.
It's a very nice kit and goes together well. I always attach the front and rear bumpers, but not the rear fenders before painting. That makes it easier to paint inside the rear coves.
Hmm, I guess I'm mistaken. I was going by my personal experience. I had a 70 Mustang Grande and it didn't have the roof mounted seat belts. I now have a pile of junk project car that used to be a 70 Mach 1 that doesn't have them either. But it also doesn't have a headliner or much else. So I stand corrected.