340 lifter noise

i still have the other pushrods that are 7.550 should i try it with these?is the preload the distance that the plunger actually moves down from the top? it should be in the .030 -.040 range when the cam is on the flat side of the lobe right?
its just that i wish i would have kept the original head gaskets that i took out and through away without measuring,i gues they could have machined the block somewhat and thats messing me up but i dont believe there are any gaskets thinner than the .024-.028 mopar ones are there.