Spindle ID

I disagree with that.
Take a look what a "B" body spindles looks like, and what an "F" body, Aspen & Volare spindle looks like in post #6.
I'm not that familiar what M or J body cars, spindles look like.
In appearance, they have differences, even though they all will work when doing disc brake change overs on older cars.
'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 which includes '73-later B and all F/M/J. Coincidently, all have a rubber isolated K-frame