Bruce Robbins wrote:
"I was trying unsuccessfully today to get a Campagnolo Gran Sport mech from the early 1960s to accommodate the 28 tooth cog on a five-speed freewheel. Is it a question of footering about with chain length or am I wasting my time? The front chainrings are the usual 42/52."
I suspect that the challenge is the 10-tooth difference in front. Bikes of that era typically (in my experience) used a 3 - 5 tooth split in front (47-50 was common). Since the Gran Sport has its pulley pivot centered, with a real short pulley separation, it won't wrap as much chain as the later Record -- which also has the pivot offset forward.
Sorry 'bout that, and hope this helps.
harvey sachs
McLean VA