TTI Exhaust with offset shackles?

I have a 318 bored 60 over and stroked, making 450 hp. I bought their system, Headers right on back to polished tips. In 2.5" X pipe not H pipe. there header flanges are the thickest ive seen. hangers are second to none. my engine builder wouldn't let me use TTIs 3" exhaust . his opinion was it wount help don't waste money or space. I guess having an exhaust that's too big for the volume off air being moved through it might be like having open headers. open headers don't help performance in most cases.
I might have some pics of the system on my members restoration page.