Just a thought I was having. After the Cyclone MkII RD on my restored Centurion broke, and the freewheel started making really bad noises, I decided just to respace the frame, run an 8 speed cassette, and put a Tiagra RD on the bike.
It works fine, but I've almost exceeded the capacity of the shifters. (Suntour Symmetric friction shifters.) It's standard Shimano cable pull, where the first shift out of the smallest cog takes the merest "twitch" of the lever, but that last one to the largest is a whole lot of real-estate to swing through.
I'm wondering if the SRAM rear deraillers might be a better match for friction shifters in general, given the 1:1 or 2:1 constant cable pull across all ratios.