Last itme I set up a tuned pipe was a while ago but the process is not going to change. Put teh full length header and pipe on your engine with the prop you intend to use and get your tach and tubing cutter. Tach your engine and then shorten your head in 1/4" increments until you see a drop in RPM at full throttle.
There is a nice write up on the proces here
http://www.macspro.com/tuning.asp