So off with the SunTour mech and shifter and split the chain again and out with the rear wheel. I had to shorten the chain by about 4 links but it all came together well, I couldn't work out why the cable kept slipping out of the clamp and then I realised that the clamp enables the cable to be wrapped around it, it does like some tension on the cable to work effectively, but with some fiddling with the stop screws and cable tension I've got it working a treat, I can't believe how well it shifts for a design that dates back 70 years. Mine is a 1963 version (no cable adjuster) which possibly means that although the frame is dated 1962 the bike was built up the following year.
So a short test ride in 30c heat
but it performed faultlessly, not quite as smooth as the Suntour mech I removed, but not far off and it's really nice to have the original equipment back on the bike. It just makes it feel that bit more special.
I thought the concrete sheep would make a good photo opportunity!