It worked!
I bought the 060746/KIT Commando Drive Plate Assortment "shim kit" from OldBritts. It comes as three shim plates; one 0.060", one 0.070" and one 0.078" thick. OB will take back and refund the plates that you don't need, obviously so long as you don't damage them.
So Dave and I tried all three and decided that the 0.60" shim was the best fit and immediately upon fitting the plates we noticed a huge difference in the clutch pull action. The thicker 0.70" plate was just a little too thick and took the spring too far over center. The .060" seemed to be the best size so fitted the shim at the very back of the clutch basket and reinstalled the clutch.
Attached below are some pics of the process.
Step 1. Shim Kit from OB:
Step 2. Empty clutch basket:
Step 3. 0.060" shim added first to the rear of the clutch basket:
Step 4. Final (lighter) Barnett plates added:
Step 5. Final pressure plate added:
Step 5a: Another pic to try and show that the pressure plate is flush with the outside 'teeth' of the clutch basket:
Step 5b: Another pic to try and show that the pressure plate is pretty flush:
Step 5c: Another pic to try and show that the pressure plate is flush:
Step 6: A pic to try and show the gap between the spring diaphragm plate and the groove for the circlip that holds the diaphragm plate in:
Step 6a: Another pic of the gap between the diaphragm plate and the groove for the circlip:
Step 7: Clutch reassembled and adjusted and immediately noticing the clutch action improvement!
Step 8: Go for a little ride around the neighborhood to test the clutch...
Step 9: ....keep riding for 20-30 miles because you're so happy with the clutch action!!
Step 10: Come home a very happy chappy!
Thanks for all the advice guys!
Cheers
Mike