You'd have to spread the frame, at the very least, to fit the hub. It's 170mm wide. Not sure if the rim/tire combo would clear. The rim is 100mm wide, if that helps... you could measure where the rim would be and see how wide the frame is there.
To put a 20x4 rim and tire on a 60s muscle bike you would probably have to weld/reconstruct the entire rear triangle for tire clearance, and weld in a wide bottom bracket shell to the inside of the existing bottom bracket shell, the fit is not exact so you would have to shim it with an intermediary length of tubing before you weld. It has been done before.