2.5'' on 318?

I will be redoing the exhaust on my car as soon as the engine is pulled to get the body repainted. With the engine out I was planning on installing a set of TTI headers. I was going to build my own exhaust system with 2.5" tubing, from header to X-pipe to Dynamax Ultra Flows. Is that to big? It is not a stock 318, it has been bored to 321 ci., 600 cfm 4bbl, mild cam, and soon a 3.91 sure grip.