LA engine valve cover leaks

I feel your pain- I don't ever remember having that problem with the LD340s, Tarantulas or Offys I ran; and I paired them with all the usual M/T, Holley and Cal Custom valve covers of the day. Never an interference issue.
All I can suggest is that now all anybody runs are AirGaps and Victors, and Eddy likes to cast them with extra meat up top for guys who want to open the ports up... instant interference. Or maybe they have to cast them thicker now to allow for more variance from the offshore foundries?
Maybe newer style "fabbed" valve covers don't have that issue, I dunno. Never liked that look- I'd rather run stock steelies than those.