I have an 80's model Schwinn world road bike. It has a double crankset, not even a compact, just a double. I live in a very hilly area, and I really need the extra gears a triple will offer. I have stem shifters on the bike, so indexing is not a problem. I have an old walmart roadmaster mtb laying around, and I want to know if it would be possible to change the crankset from it to the Schwinn. I am only going to throw the Roadmaster away anyway, so would it be possible? I don't mind switching the bottom bracket too, I just don't know if it can be done.

This is going to be a temporary fix until I can afford a new, (or moderately new) road bike for myself, but since I already have the parts I thought I would give it a try.