The RPM Air Gap 2.0 on my 454 is made to have the heads plumbed from the top rear corners on the manifold crossover to the front corners on the manifold, just to reduce the "hot-spot" there, so I did it. I'd do it, it won't do any harm, actual bennefit, I am uncertain.
Are you running in a jet or an I/O? I have never run a t-stat but my water flow to cooling is restricted by being valved at the pump. Regardless of water temp I run a decent engine temp, but it does vary IF I go out real early in the year, or real late, by about 10* 90% of summer, no change. My engine runs about 170 at idle, 130 flat out, and I have never noticed a condensation problem.