Has this engine been sitting a long time???? poor maintinance over the years???
Is the rocker shaft assembly getting enough oil??? How's the oil pressure??
Not knowing the complete history of this engine, one possibility is that someone in an attempt to get rid of a colapsing lifter issue, tried replacing some of the lifters with solids. It's been known to happen.... Or you could just have some gummed up lifters from sitting awhile...
Colapsing lifters on the 235 is a very real occurance. I've had it happen to me repeatedly, as well as several other guys I know. Can't say I've ever heard of it happening to the later engines.
The only sure way to cure it is to switch to solid lifters.
How are you adjusting the lifters? with the engine at low idle and warmed up, one at a time, back off the adjuster till you start to hear it tick, then tighten about 3/4 turn. NOT 1 1/2 turns like some manuals show...
