In my own limited experience: I ran a '73 Motorhome 440 with steam holes in the deck & heads, however, my Fel-Pro head gaskets blocked off the holes. I had no noticeable problems with cooling.

My particular motorhome heads took a different style of spark plug compared to a "car" head. Tapered seat with no gasket as opposed to a flat seat with a crush washer. Not sure if its a similar situation with your later 452's but thought I'd mention it anyway.