If it is an older American oversize bb, then the converter above will work. You can just tap out the old cups with a screwdriver, they will pop right now. The converters work perfect, I used one on an older conversion I did at one point. The only problem I had was that the shell wasnt perfectly round, so I had to hammer the converter in. The tricky part was making sure that I hammered both sides in straight so they could screw together. Just go slow and be careful.

The other option would be to just use another 1 piece crank...not my recommendation...but another option...