That impeller or the improved water pump kit should be in stock at most BRP ( Evinrude ) shops.----That is if you can find one.----In Canada---evinrudeparts.ca----Is one source.
Check the NLA fitting and grommet found at the top of the water tube.----If bad you have to find a used one or make one.-----Check water jackets for debris / old impeller bits.------And if there was severe overheat post your compression numbers.
A 15" pitch would be a good starting point.----Is the motor in good shape?----For reference in the future do a compression test.----Post the actual values here.
Do you have all the parts?----The pulleys / cable / spring ?------Have not worked on one in a long time.----Magneto plate should rotate CCW when opening throttle.
