John, that rad support comes really close to the hood when closed. I don't think that plan is going to work. Close the rad top with the smallest cap you can and add a filler spout in the upper rad hose. Done that many times with no room.
I haven't checked for how much clearance there is in that spot yet but I know you're right about it being a close fit. I'll probably wrap some plastic food wrap around some clay and position it there before closing the hood so I can get an accurate measurement. With the big hole already chopped in the hood for the blower, I figured nobody would care if I needed to remove some of the hood's under-structure. I think I'll have clearance if I can adjust the height to be just above that cross-member.
We did kick around the idea of running an upper hose filler but preferred to keep the fill location on the radiator if we can. - We are still considering it if we strike out on the other plan.