RE: Welcome to Club SAITO !
The 82 gasket set is only $4.50 but if all you need is the Viton O-ring you would soon wind up with lots of extra gaskets.
What all is needed to replace the plastic backplate on the 82 with this newer aluminum one? Just the backplate? It is $9.50 which isn't bad.
FA-82B Rear Cover: AB, RRby Saito Engines (SAI82B17)
Thanks,
Ernie Misner