I've always found the R31 rear calipers shitful to work with. I'm sure they're only the common disc conversion because they bolt and you have a handbrake, so still street legal.
I was quite fussy setting mine up, but still have the issue with handbrake cables running close to half shafts, bleed nipple not at top, so have to unbolt the caliper and rotate on disc to bleed. A bit annoying.
For a road car with occasional track use, it's a bit of effort for no real gain and a handbrake set up that's not as great as the drums.
If your drums are ok and you can adjust your brake shoes up if/when needed, then perhaps not a bad option to stay with drums..