Proof? Actually no... If they are fake plates though, they were used one time & one time only for that picture, then they were
never seen again. I've talked to
many guys who trained at the original Gold's Gym, including Joe Gold and nobody ever saw any fake plates.
Especially those old school thick-lipped 45's being used in the photo. Those would be tough to make out of wood.
So "proof"... no, but they are real.
Edit: I'm guessing that is either Denny Gable or Ken Waller.