To keep peoples heads from exploding, please tell us what crankset you are using, what the current bottom bracket is.

reading between the lines, and swagging a lot, and having been through this recently with an Ofmega (campy clone) crank/bottom bracket, my guess is that you have a campy crankset, which uses a different taper than than what you can get in a shimano cartridge BB. (this is the case the whether it is british or italian thread in my experience)

If it is a vintage campy you also have to be aware that the spindle is not symmetrical, being longer on the crank side.

My recommendation is get a correct ball and cup bottom bracket or go phil wood (which is probably still less than the paint job). I spent a lot of time and some money (tried a miche sealed that looked like it would work but didn't leave chain clearance) coming to this conclusion

I know sheldon says they should work, but notes the it would not be good in higher stress situtions.

I looked at the interface between the shimano spindle and the crank set and the about of crank that was not contacting the spindle was more than I was comfortable with.