When claying heads and you have a hydraulic cam, use solid lifters. A solid lifter doesn't give do your readings will be accurate. Normally you have .080 - .100 of play in a hydraulic lifter so that can be a problem real fast. just cruise to the parts house and get two solid lifters. One for intake, one for exhaust.
Also a little tip...
Clean the piston good before you put the clay down so it will stick. After applying the clay to the piston, spray the clay with WD-40 or coat it with oil or ATF. Then spray the valves and combustion chamber so it won't stick to them either. That way the valves won't stick to the clay when they come down and screw your progress up.
------------------
http://members.aol.com/BOSSC351/index.html