I found that you can swap out old British cotter crank BBs with 1980's vintage Schwinn BB cotterless cranks. This is being pulled from two year old memory, but I think it was a Schwinn Sport that I used. I did it on two bikes and it worked perfectly.

I replaced the BBs on a Hercules ten speed and a Raleigh Grand Prix ten speed. Both had cottered cranks and both were from the 1970's. Like I said, I replaced them with cotterless BBs from made-in-Taiwan Schwinn Sports.

Everything fit perfectly with no need for alterations or modifications.