596 heads spring installed height too low

the shims were there because the old springs werent giving the required pressure to control the valve/lifters at the expected rpm. there is room to lessen the hight depending on lift vs spring max compressed hight before coil bind/stacking in order to get more pressure from the spring.

the new springs dont need the shims, they do need at least 1.70 height, much less height/more psi will more than likely hurt the cam upon break in. imo

isky makes a +.050 or +.060 retainer for the 3/8 stem valve and common chrysler dimensioned retainer.