I've done this myself just recently, I had to do the same as "awattam" above and have a nut welded onto the bolts to get them out, the hex head had corroded into a nice cylindrical hole on most. I didn't have time to do a proper job painting them so just quickly scrubbed back what I could (mostly the lacquer peeling away) then painted over with heat resistant paint, doesn't look great but it did the job.
I also put heat resistant sealant between the plates and calipers when putting them back in, with new stainless steel bolts and stainless bleed nipples. I used a flare spanner and didn't have any problems with any of the connections, although I also spent my spare time dousing them in WD40 for a while before hand.
If you haven't got the calipers off be careful of the solid pipes on the rears, I sheared one of mine off as the fitting had corroded to the line. Not a big deal but hard to route a new line the same way around the trailing arm.
The pistons are DAMN expensive, I was talking to Andy at Promax about this and he said the reason they don't offer a refurb service is it simply doesn't add up, the costs of replacing all the bits plus the time to take it all apart and paint barely make it worthwhile.
In my case I didn't need to replace any of the pistons, even though one of my dust caps had gone gammy and the plate lift and corrosion on mine was horrendous on all 4. I just had to replace a few dust caps, one I broke the other had rusted on one side but hadn't done any other damage.
Sorry for the long post - basically don't bother replacing the pistons unless you NEED to!
Why is it you're refurbing, is it plate lift or do they look tatty?
