Im not aware of any 3.10” piston calipers that fit anything A/B/E/F/M/J/R. Sounds truck or C body to me, and those won’t fit the caliper brackets.
I could be wrong, but I’m pretty sure the only options are 2.6” or 2.75”.
If the calipers aren’t stuck and don’t leak I’d have no problem flushing clean brake fluid through them and running them. I’ve seen them screwed up in reconditioning, and other than the seals not much usually goes bad.
