Prop & Fuel ratio

[mikes clip on motor]

I have a 1963 Seaking 15Hp. motor model GG18802A that needs a new prop. There are no numbers on the old one. Boat will be used at 4000 to 7000 ft elevation. Need to find size and or part numbers I also need to find out what the oil to fuel ratio is. Haveing a hard time finding any manuels for this old of a motor. Thanks Mike