Motorcycle Repair: TRIUMPH BONNEVILLE GEAR BOX, drive sprocket, triumph bonneville

Question
MY ETERNAL QUEST.
ON A 1970 T120R BONNEVILLE, IS THERE AN AFTERMARKET SET OF HIGHER RATIO GEARS OR ANY WAY TO SWAP OUT THE FACTORY GEAR CLUSTER WITH THE LATER FIVE SPEED TRANIES?
I HAVE PUT THE BIGGEST DRIVE SPROCKET ON THAT I CAN FIT BUT I DONT WANT TO PUT A JAP REAR WHEEL ON WITH FEWER TEETH ON THE HUB TO REDUCE RPMS.
IS THERE IN FACT ANY WAY TO DROP THE RPMS DOWN TO A MORE SEDATE LEVEL WHEN AT HIGHWAY SPEED?
IT MIGHT HELP TO REVEAL THAT I AM RUNNING A BOLT ON HARDTAIL WITH A 16" WHEEL.

Answer
You can make the later 5 speeder fit with a little 'jiggery-pokery'but the final drive ratio would remain the same, all that would achieve is a closer mid gear ratio, as standard though, top gear should be good for 112 mph so I'm surprised that you find it too low?