Correct- no manual valve adjustment was possible since these engines had hydraulic lifters. The rocker pivots are torqued down tight on the hydraulic cam 351Cs. On the Boss and H.O engines, the entire valvetrain was modified by Ford to accept mechanical cams, adjustable rockers, pushrod guide-plates, single-groove one-piece valves and hardened pushrods. Each rocker stanchion was cut down by the thickness of the pushrod guide plates, and since they are at compound angles to each other, this is tedious to do even on a milling machine. All factory Boss parts are still available but since it replaces every single piece on the heads, its kind of expensive. Iskendarian Cams made a special cutter that could be used in a drill press to trim the stanchions. Crane Cams now sells a conversion kit that uses their own pushrod guide plates that have replaceable hard-plastic inserts without cutting the pedestals. And being plastic, std non-hardened pushrods can be used.This is mainly for adapting full roller rockers to non-race engines to lower friction & reduce oil temps.
