Welcome to the new Wizard Outboard Forum.
What Mercury piston rings match the WG7 rings that has a bore of 18.34. Will mark 10 rings fit? Did the WG7 have a separate gas tank or was it on top of the motor? Are there any pics of a WG7 that can be posted?
Specs show the same 2-11/32" bore and 18.34 ci displacemant on both the WG7 and Mark 10, so I would guess that they use the same ring.
I have a WF7 and it has an on-board tank. I would guess that the WG7 has also.
JW in Dixie