Originally Posted by Chombi

Six would still work with a regular width chain but you would need to go to a narrow chaiin with a 126mm spaced 7 speed system. I put togther a 7 speed system for my bike last year with a Maillard Compact Plus freewheel and it shifts beautifully with a narrow Sedis SL chain. which was sold by Campagnolo and Mavic and also re-branded later as a Sedis/Sachs narrow chain. The classic narrow Sedis chain pops up once in a while at eBay if you want to get something period correct, but IIRC, many have noted here that they also have good results with new narrow chains from SRAM too for seven speed systems.