Coolant bottle for engine swap

I'm deciding how to run the cooling system for my LSx swap into my 88 Z31. My radiator does not have a fill port (the stock VG30ET fills from an extension of the lower intake). The 2002 5.3L engine I have originally fills from the radiator.

My buddy insists that I have to run a coolant cap and bottle that is the highest point in the system, but I don't see why I need to. Won't the pressure spring in the cap do its job regardless of where it is placed in the system? Otherwise, wouldn't your car start dumping coolant everywhere when hit some hills?

http://www.az-zbum.com/images/engine.z31.v8.1.jpg

That isn't the same engine, but he has a filler that I would like to use with a stock Z31 overflow bottle. I realize that bleeding air from this setup would be a pain, but my underhood space is at a premium. I am running my heater core, I cannot tell if the Z in the picture has it hooked up or not (if it even matters).

I can't think of a reason why the overflow would need to be higher, unless your also using it as a radiator fill point.

Generally the fill point is the highest point in the system to allow the system to self bleed as much as possible.


The set up in the photo looks like a fill point is fitted to the top hose?