If the bottom bracket bearings are smooth, then remove the spindle and take it to a shop. Find another square-taper spindle (doesn't have to be Shimano) with the same basic dimensions between the races. Get some new bearings too. Grease it all up and put it back together. Put on your cranks of choice.
Gotcha will check my spares. One of the crank arms is slightly bent. It has a bent regular bolt acting as a cotter bolt. To top it off pedal threads are stripped.
This is my first folder, wanted something inexpensive to use as a trunk bike. First impressions are it feels lighter than it looks. Even with all the steel. Folding mechanism is pretty solid. Its a 5 speed derailleur setup. Calipers on these things have a lot reach down. With the 490 rims it looks maxed out in the slots. Eyeballing the slots seems like going smaller would be a better bet than going 507.. if one were going to a standard size alloy rim. Rims seem fine though so may leave them.
Filed the cross-threaded threads down and managed to get a pedal screwed in somewhat straight. Rode it to get lunch and it I like the way it rides. Will work on a better fix later. Fitted a steel rear rack and rear fender too. Weighed it. Its 36 odd pounds.. must feel lighter to me because its compactness makes it easy to lift.
Its a beater with scratched up paint and pitting, but it was cheap. Also is missing some parts.. You know what I'm happy with it, think I'll leave it as is with the ugly crossthreaded bmx pedal and stock cranks and steel rims.
What drew me to this thing was the age and large wheels. Personal preference for a vintage look and 490mm tires rather than something modern or smaller tires. Have noticed pedal strike during cornering.. no problem though, I'll get used to it.