Caliper Help!!

I'm trying to rebuild a set of 4 piston kelsey-hayes calipers. The fittings are so rusted, I can't get them out no matter what I do. I've tried every lube on the market from WD40 to PB. they won't budge. I'm chewing them up with the vise grips. I guess I'll have to drill them out and re-tap them. Does anybody know the thread size for new fittings and bleeders? Thanks!