To close this down gracefully I'm binning the extensions
Reasoning
With my weight and resulting mean shaft angle I am concerned about wear and premature failure of the u joint
The angle may introduce vibration and/or inefficiency in output due to changing in rotation speed during the cycle
I'm going to focus on getting least angle with and without rider.
I will get ride height if needed, with tyres, but I intend moving the pegs to get the clearance I want, this also keeps the centre of gravity low.
Thanks for all your help.