As long as all the inputs are the same.

Fuel sender isn't going to change with 20v conversion
Temp sender will change, you may have to fiddle around with that - i.e. plumb the old gauge sender into the new cooling system
Speed sender isn't going to change with 20v conversion
Tacho input will change so you'll have to find a suitable place to pick up an ignition trigger to get the tacho working.

That's pretty much it, really.