[Marshy]

The Vortec heads use a raised ceiling port that the old manifolds won't line up to, even with some grinding on the ceiling of the lower manifold opening can't account for the difference without welding/machining IIRC. Your best best is to call summit and ask them if they have an intake that will fit your heads and have the front oil fill tube. There might be something out there that's easily over looked.

Regarding issuing a 72cc combustion chamber, that's a really good way to go to get your CR down. However, I wouldn't recommend it blindly. Ask your builder to give you the deck clearance and piston relief volume so you can estimate your CR now and with the 72cc heads. You should (ie your builder) needs to know the deck clearance to choose a head gasket anyways so you aren't asking an oddball question anyways.

Did you chose a cam already? I'll review if you did... you might want the smaller heads if you are using a large duration cam. That's where you get into dynamic compression which dictates what octane you need, not necessarily static compression.