Exhaust opinion

I forgot to mention;
you can do a pressure test just ahead of the muffler. You are looking for a maximum of 4psi at WOT, as the engine moves thru it's peak efficiency rpm somewhere between 3000 and 4000 rpm in your case; Less is better. Do not buy into the myth that an engine needs some backpressure. What an engine really needs, is a hi-powered vacuum cleaner on the end of the pipes!