My 64 chevelle is an open type unit that has no tank (spills onto the ground) Currently I have a 13 lb. cap on the radiator. Is there any difference on the radiator caps for this type system as opposed to the ones with the overflow tanks? Would it hurt to move up to a 15 lb cap? Reason I am asking is I want one of those billet specialites caps to match my valve covers and they do not specify so I thought I would pose the question to people that may know if this would be a problem

If your radiator is in good condition a higher pressure cap is ok.
I added a coolant recovery system to my 65 with a higher pressure recovery cap.

What is the visible difference between a recovery cap and a non recovery cap like my system has?

this is the link to the cap I am wanting, if you look under the tech info it states that 7 lb is for pre 1966 vehicles, that seems too low but I am afraid the 16 lb will not operate correctly

http://www.billetspecialties.com/item.asp?cid=7&scid=87&pid=211