Generally things workout cheaper if you can get stuff off the rack . I couldnt see evolution getting stuff made especially when there's something thats going to do the job thats nearly the right size . I have one of these engines with the macs muffler on it and dont know where the oem one is to measure ( always a option for you and may even be cheaper if you need to buy the tube and get someone to weld it . Most fabricators and welding shops have a minimum charge to keep time wasters away . When I was doing this for a living I would always say that I may fix it or f@#ck it just in case the stuff wont weld properly which maybe the case in this instance .If it was me I would get the macs muffler and leave all your troubles behind . Good luck with what ever path you choose from the pope