I was lucky enough to meet and talk with Ed Iskenderian several years ago at Eagle Field. He is an amazing guy with a lot of knowledge about many different subjects, as I found out. He was only 90-something at the time and attracted quite the crowd in the pits. This was a disgusting situation...
For some reason I think Holmes = original Cal Custom? Could easily be wrong. Showcars used to have some inexpensive imports that were not too bad. I think Moons, Weiands, old Edelbrocks would be my favorites.
I guess their thinking is that an "endurance" engine should/would be using a less stressful camshaft and thus could use the lighter rockers. I guess such an engine might also be more likely to have stock covers? Who knows?
They just didn't want to call it "street" or "street/strip" for some reason.