I also posted that on BB and one comment from a guy who is just installing a Chevy Corvette engine in an E32 is:
quote

I'm not sure of removing the rear seal to allow venting, it's always been my understanding that the area at the base of the windshield was a high pressure area. This should put more air into the engine bay- seems like a good idea. The most benefit would be after you park the car, then the heat has somewhere to go.