Thanks to Metalman and Anorak Bob for plans. I have now digested and adjusted for the Hercus set up. I think I will give it a go as it will test my ability to produce nice running fits, press in bushes etc.

Not sure about long drilling but Google pops up plenty of people selling long drill bits. I may make up a complete countershaft clutch outfit and keep my Hercus one intact (just in case).

Not sure how to produce the keyway on the countershaft and in the countershaft pulley so that it slides nicely without play as the clutch is engaged and disengaged. I may also try for ball races instead of cast iron countershaft bearings as I can't find any one selling the cast iron bearings at the moment.

David