before you go looking for this you need to be sure that you have the older style crank case.
it will have a seal housing bolted to the back on the case and the coupler will be inside the last seal. look at it or post a pic.
if this is what you have i can give you part numbers for the seals. as for the seal housing gasket it is discontinued. so unless you can find a NOS gasket you will have to cut one your self.