Get the Macs one piece muffler. It saves you 6oz. over the OS powerbox and gives the same or slightly better performance. Do not get a header and tuned pipe as they will kill your midrange.
[link=http://www.macspro.com/onepiece.asp]Macs One-Piece #7310[/link] This is the one you want. Get a better price at a hobby shop or eBay. For props I like the Xoar 18x6. The APC W's are heavy.