'73-4 or so B body spindles are the same as F/M/J spindles except that F/M/J are scalloped out between the caliper mounting holes on the spindle. I think they changed to the scalloped out style in '75. To put it another way, except for C body spindles, there are only 2 RWD car spindles for '73 and later. They are:
1. '73-later A and E spindle.
2. Everything else. '73-later B and all F/M/J