Any CAD program should be able to do it. Basically get and exhaust gasket and get the dimensions off that so that is pre-portmatched, length of primaries will be down to how much space there is, length of secondaries anyones guess (theres probably and equation floating around the interweb). Diameter primaries = port diameter secondaries 5mm larger? tapered collector 51mm (2" its a 1.3 remember)