340valve train noise with new head gaskets

i just put new felpro 8553 pt head gaskets in.now all my rockers are loose,they rattle on the flat side of the cam.and the push rods rotate freely.what kind of preload should be on the lifters .these are factory non adjustable hydraulics.napa called felpro tech and he gave excuses,i know there are thinner gaskets out there .did i make a mistake buying the felpro gaskets or am i doing something wrong? lifters never left bores rockers are l and r facing them and all are torqued down,also whats right way to block heat crossover i have a m1 dual plane and antifreeze cam out around heat croosover area only on both sides.
tks for any help