You don't have the plenum when you remove the top, just the runners. I've got one here that's going to use efi throttle bodies, but a dedicated manifold would be nice.
Gotcha, depends on the design/manufacturer I suppose. last tunnel ram I had a good look at was a GM one wich had the runners & plenum cast together with a removable top plate.
Could get a bit cramped with the runners all bunched together.