i was looking at another forum thread of someone doing a restoration on a Seville and they installed a new prop. they used a Quicksilver Black Diamond XT-14 1/2 21 Pitch. He had an Alpha 1 outdrive on his boat
Whichever prop you go after will be your starter prop and then go from there dialing a prop that will make the motor to run at least middle to max wot frevs as usually loaded. It's much faster going for a spot on prop maximization from a previously tached prop or lost one than begining with a wild guess one as a starter prop.
A pity that lost prop was never tached previously to buy same or go from there..