Hi Mike,
I have a GT6 MK2 with 3.27 diff. Just before Christmas I paid Mike Papworth to install one of his 25% J type overdrive kits. Very happy with the outcome. Now 2000 revs at 50 mph. Did two European tours this year and glad I had the OD fitted.
Even the 6 hour trip to the Peak Valley Run this year was so more relaxing with the overdrive. Especially pulling the trailer full of camping gear at 50 mph.
Regards,
Nigel