I put the seat belt planet ones in my 60, 3 pt front and rear. I wouldn’t do it again; I’d find a suitable used or other vehicle option.
My SBP belts are a pain to use. The retraction spring is so tightly wound that if you unbuckle and aren’t holding the male end, it shoots off into to window. I’m used to this but my passenger window tint is all scratched up from the buckle smashing into the window at 237 mph.
Next, the lock on them is super sensitive and the angle of the belts make them “self tighten” while you’re driving. While driving, I routinely have to gently pull the shoulder strap out and feed it back through the male end to give me breathing room. This is like every 10 minutes, more if you’re on a bumpy road. Almost daily, I have to unbuckle while driving to completely retract the shoulder belt and then rebuckle.
For the rear, I put car seats in regularly. They are near impossible with the SBC belts because for some reason, putting a car seat in is the ONLY time the seat belts won’t lock.
The plastic housing over the reel portion is pretty big too and wasn’t easy to fit in the rear without interference to the seat when folding.
Honestly, once I’m done with more pressing projects, I’m ditching the SBP belts.