Truvativ makes an adapter to use english threaded bottom brackets, but might be simpler to stick with a 1 piece crank. You will have trouble trying to make that threadless fork work because you can't just find something new to fit. These kinds of Schwinns had larger diameter head tubes that fit 1" english threaded steertubes. You"ll need a complete headset and threaded fork.
Info:
Parts for older American Bicycles