RE: New! Dug out my dads old Gas or Nitro boat!
I'm assuming its an outboard engine probably mounted on a tunnel hull.
good plug to use would be K&B 1L. as for Nitro use what you have available in your area, 20% nitro or more with 14 to 18% oil content.
I had my K&B 7.5 running on 10% Nitro.
You won't find too many boats with a clutch unless your looking for a toy or going bigger with a gas engine and again not everyone runs them with a clutch, I don't.
if the motor was stored properly like you said fuel drained, after run oil or another type of oil put in the engine for storage it should be good to go.
You could take the engine apart to ensure all is ok, if you feel up to the task.
Dan.