Well. On the D-66/64 I have, 2 Carter's sit on it and operate fine. Adding the adapters would just require the gasket. Hooking it all up there after, well.....
I don't know about Holley carbs on the D-66/64.
I just got done collecting all the big parts to a future 6 pack build. Click my screen name and see it in the picture box. Next are some ProMax parts.