It is pretty common to mill the sides of the plenum for relief for the valve covers.
I know that Jeff @ MCH does this when he mods the internals of the MP Cross Ram.
My

Mark


1996 Ram 1500 Sport
1968 road runner
1952 Sears Allstate licensed, pump gas, Hemi 5.98 @ 115.73 1.33 60 ft. The best is yet to come. Painless Performance / Street RODDER magazine Top 100 for 2019