[sspano01]

not sure about the "replaced with hydraulic". but a flat spot is probably easy to find. pull the valve covers are rotate the engine over with a breaker bar. look at each rocker arm. if there is really a flat spot, there should be one rocker that is noticeably not moving as much.

i had a 1973 malibu in college that i bought for $50. it had a flat spot, no lobe on one of the exhaust values. it sputtered and knocked and did all kinds of goofy stuff. a new cam fixed it. pulling the valve covers made it easy to see that one rocker arm was not moving