After lots of research, I decided to replace the original cottered cranks on my Raleigh Grand Prix with Velo Orange's threadless BB and Grand Cru compact double. I went with a 118-mm spindle, since that's what was recommended with this crankset.

Removing the old coffers actually proved a snap -- done in about 10 mins with a c-clamp.
But the new BB was a battle because the Park Tool lockring wrench constantly slips out of the not-very-deep notches on the outer rings of the BB. Finally though, after much elbow grease and a nasty looking gash in the previously perfect paint on the BB shell, it looked seated. I put on the drive side crank and immediately knew I had a problem. The arm is close to the chain stay, and the chainring is not even clearing the drive side cup. I removed the BB and see now that the threading on the non-drive side is stripped (the threads don't engage the BB shell but rather, the expanding cup things) and this was not totally tightened.

This leaves me at an impasse. Do I:

1) Order another Velo BB in a different spindle length. The company offers 122 and 127 lengths.
2) Order another in the same size and try not to strip another.
3) Be thankful I didn't totally f-up the frame (it's my father's and this worth a lot more to me than your average $35 GP), grease the threads, and reinstall the heavy old cottered cranks.
4) something else.