You are correct, the silver ring goes on the top, black on the bottom. The end of the piston rings are tappered one way up so that it will only fit over the locating pins in the piston one way, allowing the rings to fully sit in their groove.

The original Piaggio air-cooled cylinders do not use a head gasket, they use a smear of high temperature sealant, we would not recommend to use a head gasket because this would change the compression ratio.