If the engine was run on leaded gas back in the day, it should be fine. If it had a valve job after unleaded gas became the norm and exhaust seat inserts were fitted, it's fine. If it had a valve job without seat inserts and it's not driven hard, it's okay. If it had a valve job without inserts and it sees a lot of extended high-RPMs, that can be a problem... but I don't think lead substitute will prevent much of anything.

Just drive it -- the only bad thing that can happen is that it will need seat inserts, and that's also the permanent fix. No reason to do that as a preventive measure if there is no evidence of seat recession.