So, if I'm reading this correctly, my 360, using the 340 manifolds, will produce 315hp max, and changing to the awesome (but expensive) TTI headers gives a gain of 12hp. I understand that if I were racing or just looking for bragging rights then sure, TTI headers are the way to go, but typical street use wouldn't make any practical difference. And yeah, I decided a long time ago that if I were going to use headers, it would have to be TTI for fitment, especially their slip-tube design.
I still think that using 340 manifolds on my mild 360 build is the right thing for me, but who knows? I may run into some money later or decide to up the power on the build and go a different way. In any case, I really appreciate the information from all of your perspectives!