This is all vintage 1975 stuff, all of it. The bottom bracket is a Phil Wood. The crank is a Campagnolo Record. The rear derailleur is a Nuovo Record. This freewheel is a Suntour Pro Compe (I also have a 14-22T Dura Ace 5 speed). The chain is a drilled Regina Oro. The frame is spaced in the rear at 120 mm.

All the original equipment gear listed installs and lines up with zero problems. It's when I try to "upgrade" to six speeds that the difficulties arise.