Escape, the problem is at the throttle end where the end of the cable terminates in a barrel nipple.
Talking today to a chap who restores pre war motorcycles I asked him how does he source the correct control cables, ‘simplek he says ‘I make ‘em!’
So onto his recommendation to a company called Venhill
They supply kits for making cables https://www.venhill.co.uk/cables-amp-components/car-cable-kits/universal-car-throttle-cable-kit-ven-ukccblack.html
Or parts to modify existing cable like this https://www.venhill.co.uk/barrel-nipple-38in-od-x-12in-bn1013l.html
I'm not sure if the existing cable is long enough to fit a barrel end on and relocate to the new throttle body (on the SU’s fitted to the 3.5 the throttle linkage is at the rear of the inlet manifold, on the Thor manifold the cable attaches to the front of the inlet manifold)
We shall see, but hopefully that problem should be easier to solve now