Radiator Overflow Reservoir

['68OrangeSunshine]

After getting a tip from a completely different thread -- that Radiator overflow bottles from a Mid-'70s Nova fit inside the fender well of the '67-'72 truck's doghouse -- I bought one from Jeg's. Now I'm getting the other needed fittings to complete the mod.
The cap for the bottle is a Dorman part, but I didn't see it on the HELP shelf in my local Auto Zone. Tubing I can get from Ace Hardware.
The real question is what radiator cap do I use? I have a Stant 16 PSI with the red plastic sefety lever. It's so old, it was made in the USA. [Remember them?] I have heard comments that the plastic ''safety lever'' can break off -- leaving the cap stuck on the filler neck at the worst time. Never happened to me, but there's always a first time. Also the Prestone people tell me [on the side of the jug of anti-freeze] that the cap should be replaced every year.
Next item: Is 16 PSI too much for a 292 L6 w/o A/C? I used to run 13PSI, but last time I needed a Radiator Cap STAT, I grabbed the new one. It was 16 PSI.
Radiator is copper/brass 3-Tier core and is the wider V8-type for this vintage.
[The narrower L6 radiator shapes were no longer available. I only had to move out the radiator brackets to the wider position. Hoses were flexible enough as to not be a problem.] Not at all a disadvantage, since in Arizona, especially in Summer, more surface area is better.
Application is a '68 Chevy C/10, 292 L6.