I think for the heck of it, I'll be putting a ball-valve in. I'm going to do one to the rear heater box too. They are both easy access (now that I've found them and know which ones are which). One from under the front wheel well (for rear heat) and another under the hood (for hvac box).
Plus my Ford tech will be here Wednesday to put his manifold/gauges on my lines to check'em. Better safe then sorry.