Hey Bogie,
Can't help you with the year (I have owned ones with SN earlier and later than yours) and they are all the same except for earlier ones have ignition points.
I did not even get asked for SN when getting head gasket and other misc gaskets/seals from my local Honda shop.
I hope you can get her back on the water but If you decide to part it out I could use the upper and lower driveshafts. Mine are fused together and I can't change my impeller !!
