The K75 has three coils, so you would need two of them, if you go that route.
The K100 bikes had two dual output coils, that seems to be a route a lot of riders use if the coils are available at a reasonable cost.
Only concern with the R80 coil, is that you may get an old grey coil, as all of the twin cylinder airhead bikes used the same dual output coil from 1981, up until the oilhead series bikes came out, if my memory is correct.
My original grey coil failed at 13 years, the OEM replacement coil , the red cased one, only lasted 10 years, so I'm not a real fan of the OEM coils, I installed a Dyna 'brown' coil from a company called Motorrad Elektrik, located in the southeastern US for $86US including a mounting bracket.
