I've heard the car engines were, but not the trucks, only some of them. Can you tell from the pic above, if that is Mechanical or Hydraulic?
" . . . , only some of them [were]"
some of what were what?
some lifters on truck engines were hydraulic?
or
some truck engine (58-63) were set up for hydraulic lifters (but no truck engine had hydraulic lifters from the factory)?
Someone might have put hydraulic lifters in 1958 and later truck engine, but not the factory.
wollfcub ID'd the lifter in your photo as being solid/mechanical.
