1966 80hp
Belt driven mag. First you are going to have to search out a manual, OEM if you can find one. Lots to troubleshoot.
You probably will not be able to find a harness unless it's from a salvage yard.
No.
Belt drive distributor. Electric shift.
Nearly worthless if the wiring is shot, especially if the original throttle/shifter is not there. Distributor cap and rotor are available, but will cost you 300 bucks.