People have been racing with this (LA) engine for 50 years. If there was enough to be gained by doing this to offset the expense, it would be common practice. Sometimes when something isn't a popular modification, it's because there is no reason to do it.
well lets look at that, how many people are willing to really look for gains for the amount of work that would take? i mean if you were serious for 2 degree's, say .260" (just a number) the work to get all the holes to line up properly, etc etc etc. i would be curious if eliminator motors are angle milled (if legal)
FWIW I believe the reason it's not needed on an LA Mopar is that the valves already open "on center". That is, the centerline of the valves is the centerline of the bore, so they are at the widest point. The small Chevy (production) heads have the valves offset from the bore center. Angle milling moves them closer to bore center which provides some unshrouding benefit. Then again, I might be full of sh*t.