All the hemi motors I know of, except the latest Gen 3 motors that I have not work, came with washers on all the plugs.
I have had some of the tubes on the 426 motor tear the sealing surfaces off completely and still work fine with the after market push in tube seals up twocents
I did try running one of those motors several times without the washer and ended putting them back in, especially on iron heads up wrench

Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)