Honestly, it's not that difficult if you have tools, space, and some time. Just follow the manual, pull the engine, split the cases, and pull the trans out. Ship the whole input/output shafts to Robinson Industries and they'll ship back fully assembled input/output shafts that just drop in. My suggestion is to read the relevant manual sections a few times before starting
Then it's just a matter of putting it back together and riding with certainty that it will not turn into a grenade under you.
You will need a good torque wrench, the Triumph special tool for flywheel pulling, anaerobic sealant, red and blue Loctite, front cover gasket, flywheel cover gasket, and output cover gasket. but otherwise, it's just a matter of unbolting and bolting up some stuff. I didn't even remove the head or loosen the timing chain when I did mine. Keep something on hand so you can cover/seal the engine while the cases are split and you're waiting for the parts to return to keep dirt/dust out.
You do not need: A clutch special tool to keep it stationary, a flywheel lever special tool, new big end/main bearings (if yours are good), or new internal bearings if yours are good.