If the engine builder said to zero lash the lifters, then they have to be hydraulics. With the motor warmed up and running, loosen each adjuster nut, one at a time until it clatters, then tighten it down 1/2 to 3/4 of a turn.

Any solid lifter needs some "play" or lash so that the valve will be on the seat for a little while to transfer heat to the seat. Otherwise, so much heat will build up in the valve that it will warp and presto....you have a burned valve and zero compression. If you find out these are solids, lash 'em at 0.025" cold as a starting point.