Originally Posted by
Simplex
If it turns out to be English, would the Shimano UN-55 be a suitable replacement?
I'm willing to bet both bikes are English thread. The Shimano UN-55 is an excellent choice.
Once you have them disassembled, measure the length of the spindle. This is the only measurement you need.
(In some cases older BB spindles were asymmetrical. If a crankarm hits the chainstay, get a BB one size longer.)