x2dry lash simply means bled down lifters so that you can measure how far the plunger protrudes into the lifter body. I wouldn't run any more than .030" preload on a performance camshaft, but that's personal preference. So i take it that you are not running adjustable rockers? You might could get shims and put them under the rocker fulcrums, but i don't know enough about magnum heads to know if this is acceptable or not. They are cheap, so i would go with an adjustable rocker.