Primitive Don

A friend has brought me an 1980s Giant made Schwinn World Tourist with the Shimano Integer cranks and the early indexed shifting system with wires instead of cables (Positron?). I got the feeling from reading BF threads, that this system is rather screwy. Seems ok to pedal, but it doesn't want to coast very well. Wondering if anyone has any insights as to overhauling the bottom bracket?

Or is it possible/preferable to swap in regular cranks and a regular 5 speed freewheel?

Thanks!

PD