Right, finally took some pictures.
This is the clutch I got hold of. It's a bit of a lump of a thing but it seems to work quite well. The outside diameter of the pulley is 128mm so it's about twice the size of the original. There is a smaller version available but it's out of stock at the moment. I pinched a spacer tube from the PTO and turned it down lengthwise a bit so the crank was a couple of mm shorter than the clutch when fitted. I had to adjust the keyway and key slightly as it was a bit tight and find a shorter bolt.
The tensioner is left as standard but the pedal has been separated from it. I will probably be changing the brake but for testing purposes this was OK.
The brake is on in these pictures and with the rod adjusted as shown ther isn't much travel needed on the pedal anyway.
A slightly revised version of the brake pedal extension. Again this is on with the handbrake engaged and by moving the pivot forward (no holes drilled) there is somewhere for the spring. Finding something suitable took a while until I remembered I had some old exhaust springs from my kart.
This shows the 86" belt fitted and the reason why it was easier to keep the two tensioner pulleys. If I didn't the belt would have been rubbing against the gear selector.