ALERT!! SOUND THE ALARM!!..
I think that phone call i've been putting off needs to happen tomorrow. I read the info about the cooling passage differences somewhere, but I can't recall where, and I'm 100% sure I would want some kind of confirmation. The only thing I'm sure of is that they list a different gasket.
edit:
Some extra info, seems to be related to the Magnum version of the Eddy heads.
Cometic MLS w/ Edelbrock Heads - Problem