Possible. And if so, that'd be cool to have a straight screw-in product that does not need an adapter.
However, for some reason all the aftermarket manifolds I've seen have that super large hole. But they also come with a brass adapter to make up the difference. At least the Edelbrock ones too. My old Holley intake did not and I had to get one from my local Kragen (no O'Reilley). But back then they actually had it in stock too, so it must've been a common thing to run into.
There are aftermarket heater hose ends with different sized threads as well (
http://www.edelbrock.com/automotive/mc/manifolds/installation-items.shtml) but the adapter should be easy enough to find too I would think. However I'm not having any luck myself. Maybe a quick call to Edelbrock would net the part number (or dimensions) for the part.
Good luck. Seems like a good part we should have in stock ourselves. Doesn't come up often, but doesn't take much space on the shelf, or tie up much capital while sitting and collecting dust either.;D
Paul