OK so the correct tyre for my 1979 CB650Z is a 350H19 but you can't get them anymore.
The closest I can get is a Bridgestone G701 110/90/19 which is the only tyre they make for 19 inch wheels.
What does everyone else use on their old CB's with 19 inch wheels?
The cracked up old one on the bike right now is a Metzler 350/19.