I just went through re-habbing this 1977 Ron Cooper road bike, which included re-spacing the rear to 126mm and rebuilding/re-dishing the rear hub/wheel for use with a standard-spaced 6s Uniglide freewheel.

I initially fiddled with the bike's original Ultra-6 freewheel and 8s Sachs chain, during which I spread the front derailer's cage to completely eliminate any need for front derailer trim across the entire freewheel.
I used a long-handled duck-bill plier, pulling the handles apart to apply a parallel spreading force inside, up near the top bridge of the front derailer cage, so the result looks normal and the cage plates still look parallel and undisturbed.
And when I installed the re-spaced wheel with the standard 6s Uniglide freewheel, I also switched to a Shimano 9s chain, so I can now still use the entire freewheel while on the big ring with no need to trim the left/front shift lever.

I am really enjoying the light, forgiving shift action of this setup, after also lubing the shifter and cable/housing. I've been riding it hard all week and have not tossed the chain even once after making these mods, so can recommend this.
And luckily for me, this bike's Stronglight crankset has no problems with the 9s chain, that being a surprise.
I have to say I prefer this bike's friction shifting to any kind of brifters or indexed DT shifters, it's that good.
Thanks to Joe E. for the bike, and for the 13-26t Uniglide freewheel!
BTW, I switched between brand-new SRAM and Shimano 9s chains, and the Shimano chain shifts more responsively.
The duckbill plier is a very special one of my tools, and not the easiest thing to find.

This Cooper is a keeper.