I got me a 4 speed! (and I need some help!)

Autozone has some nice tachs for about $40.00 that are easy to install. Basically 3 wires -- coil and lights -- maybe a 4thg for ground -- don't remember.
Any shifter should work.
I wouldn't clean anything. Drain and fill with 90 weight fossil gear oil.
Mancini racing or Brewers performance have gaskets.
Run your stock clutch until it slips or fails. 15K is no miles.
Before I messed with machining the IBR, I think I'd look for a proper bell housing.