as for biceps, there was a joke between me and a couple of my PL buddies about a year ago. one guy would start doing curls and he'd catch some shit. then he'd just say he was just doing deadlift accessory work. lol
Is it all plywood? the sides and everything? Or are there some 2x4's or 2x6' in there too? Without knowing more about the design I really couldnt anwer.