Clark was a fraternity brother, and Millen came around fairly often to hang out and tell stories. I recall the other players and those two talking about it when they passed 500#. I don't recall about Riley taking the numbers off the plates. My guess is that although they may have stressed not maxing out, they still allowed the guys the chance to do what they could do. (Saquon did not always squat his max. as part of his workout, I'd guess, but he maxed out at times). But, that was a few hundred years ago, so....
If I run into Clark at some point around town I'll ask him. He'll own it either way.
I also recall the inventor of the Nautilus machines coming to PSU and meeting with the team and Riley. From what I recall, he was especially interested in seeing Millen and Clark lift on 'his' machines.
Clark's and Millen's exploits in practice and in games were often the source of the many stories that were told. I remember hearing about what may have been the first time someone blew up Clark on the practice field... I think it was Frank Case, another DT. The story was that in a one-on-one blocking drill, Case got the leverage advantage and drove Clark back into the shrubs by the fence where the DL was going through drills. Lots of ooos and ahhhs about that. Don't recall hearing about it happening again after that.