Thank LAB, I contacted Bob and he sells just the belt drive but not all the components needed for the entire Kit to include the Quaife 5 speed gearbox. Bob Newby said it's available possibly from P&M Cycles in the UK but I've not had an opportunity to call them yet. Thanks.
The belt drive needs a drilled mainshaft for the clutch pushrod (actuated by a twin lifter in the gearbox cover). I am not sure but presume the Newby clutch fits on a standard mainshaft. You may be able to have the shaft drilled.
One thing I like to do is extend the oil return dowels from the head through the barrels. I usually use an inch/25mm of tube for this. I then counter drill the barrels and head to account for this increase. But I also run a NH 1000cc kit and the head sits a little bit higher on the lip of the bores.
Doing this - in my opinion - means that there is less chance of the oilway being affected by piston vacuum and pressure. It also means that, if you are using a sealant, the chances of any sealant flowing into the oilway when you tension the head down is negated.
I am not saying everyone needs to do this, I just saw benefit in it and the room was there to do it.