The cover shown below is a 1971 GSE commemorating the White House Conference on Youth that was uprated by a pair of one-cent Jeffersons, with a Statue of Liberty cachet.
There's a handstamped serial number verso. Since the mailer used a private Mailer's Postmark, there's no way to tell the date of use.
The return address indicates the cover was sent by 'Steve Pavlina' of Cheswick, Pa. Does anyone know if this gent was the cachet maker for this cover, or was it someone else that you recognize?

