Hi Edboy, Muskrat.
Thanks for your replies, good suggestion about hard chroming to build-up the shaft I hadn't thought of that,don't know if they can build it that thick, Philpots the fork chroming people advertise a service for cranks.
Musky, I will probably shorten the crank, I usually run total loss electronic ignition which lasts about 3 1/2 hours with 11AH battery. I have tapped the crankcase 3/8 WHIT x 1 1/4 deep to make certain the theads do not weaken from heat cycling.
The barrel had already been through drilled when I got it so it was easier to convert the head and case than go back. Like you I tapped and plugged the head with 12mm alloy and welded and 're drilled. It's a twin carb big valve A10 head, I contacted Lani a while ago but then things went quiet, hope he's ok.
Thanks for your encouragement
Chris