The gearbox refurb parts have been ordered, if anyone thinks of anything obvious I've missed (or if I've ordered the wrong parts) I still have time to add to the order.
Triumph Clutch Hub Removal Tool from Tri Supply "suitable for all models of Triumph motorcycles." - this sounds universal for UNF
so should work.https://www.trisupply.co.uk/product/triumph-clutch-parts-hub-removal-tool/
Triumph Twins clutch locking plate, Models up to 1987 OEM: 61-3768
500/650cc (1963-73) Gearbox High gear bearing OEM: 57-0448, A2-316,68-0023,04-0098
Circlip To Retain High Gear GB1 OE Code: 70-0489
Pre Unit 4 Speed Gearbox Oil Seal OEM: 57-0946
Clutch Spring (x4), 5 plate, pre-unit OE Code: 57-0999
Primary drive chain 1/2'' x 5/16'' Links: 70
Now it's just a case of waiting....