Replacing 68mm BB on 70's bike
I've got an old road bike of the brand "American Arrow". It apparently was made in Germany, and I think it is from the 70's. So I've got a problem with the left crank, the cotter pin broke. After reading about the tools you need to maintain cottered cranks properly, I think I want to replace them with uncottered cranks, esp since the old crank arms are rusty. From my research it seems that I will need a new bottom bracket. So,
I measured the bottom bracket shell, and it's 68mm wide. It seems that that's generally going to use English threading, but since it's an old German made bike I'm not too confident. Does anyone know about this? I did check Sheldon's site about bottom brackets, but nothing about Germany..
I want to turn this bike into a 3 speed, so I'll just want one chainring. I would love any advice as to what kind of bottom bracket to get, (square or splined). I want a cheap and easy-to-work-on setup, I don't care about weight.
Is it possible to replace the 'axle' with a square tapered one (I don't know what it's called, the piece that spins inside the bottom bracket?) without replacing the whole bottom bracket? Or is this just a mess I don't want to get into?
Thanks for any help!