For my 126mm spaced rear hubs I use 7 speed Maillard 700 FWs in combination with Sedis SL and Sedis/Sachs narrow chains. The narrower Sedis chains works great with the narrow spaced 7 speed FWs. Although I also tried to use the narrow chains on regular spaced 6 speed FWs but they were noisy and shifted a bit sloppy and slow. So narrow spaced FWs works best together with narrow chains.
Chombi