Who rebuilt the engine and what kind of rocker assys were used? Stock adjustable, aftermarket rollers etc...? What heads are you using? Stock C5AE-F's? If the heads have been milled to death the oil feed slot that goes to the rockers needs to be re-grooved or you'll get no oil to the rocker assys. Is this a 65-67 solid lifter block or later service block? 65-67 blocks are solid lifter only....68 and later were drilled for hyd lifters. A brief run down of the parts used will be helpfull.