Powder coating a Gold star is a sure way to decrease its value.
If it were my bike I would blank things off myself, even down to making a metal sump plate, sacrificing a filler cap which I would seal very tightly and using a metal closure of some kind on any exit/entrance to an oil way.
I sold these things new and the paint on them was never very good to start with, sort of aerosol quality. Beginning of the end for the once mighty BSA group.
While the Triumphs used to sell quite well, the BSAs hung about to the bitter end,some of them were 3 years old when we finally sold them.
I would also wash out the oil container, its not a tank really, before it goes to the blaster,that way you have less muck for the grit to stick to.