I used the goofy new-style saito muffler (the inlet is on the side) with an old style header pipe; the one bent like macaroni. Then I attached a rubber extension to the end which fell off on the second flight (currently devising a better means of attaching.) See some of the pictures in this thread... Can you position the muffler on your 70 to be inside the cowl like I did with the Saito?? If this doesn't work out, you may need to shell out the cabbage for an aftermarket muffler. I've made my own exhausts with brass tubing, a bushing made on a lathe, and some brazing... If you're lucky enough to have access to this type of stuff this could be an option for you as well.