The S type mounting is sketchy at best. Here's a few hints. Dogleg bracket mounts under the top shock bolt so it does take up a bit more space there. Not sure how your bike is configured there, but it can probably be done. If you can find an original one and beef it up around the elbow, that would be better than buying a new one. I got a replacement from RGM and it was a bit on the whimpy side. I had my old one fixed and used it. Make sure you use a strap on the silencer side of the mount, same mounting hole size as the bracket. Here's a write up I found a long time ago, but I never used it.
"I had a problem with my exhaust mount rubbers shearing after low mileage after I mounted a set of "S" pipes on my '70 Roadster. The original design of the rear mount looks too weak to me with just two rubber mounts holding both pipes. I worked up a new mounting system as follows: I used two stud-bolts (I used 2 Norton P/N 06-4688 studs (5/16x24) I had lying around) threaded one each into the mounting bosses on the two mufflers, then installed the flat bracket that holds the two mufflers together, then secured these brackets to the mufflers with backing nuts making a rigid assembly of the two mufflers. I then made a "sandwich" of rubber isolators over the two studs using a combination of Norton tank mounting rubber washers (06-0648) and drilled-out center rubbers from the original rubber mountings. Then fit the ends of the studs through the chrome "L" bracket with more rubber washers on the far side (need smaller OD washers here to fit inside the "U" shape - had to go search the hardware store to find some), then secured with flat washers and self-locking nuts.
This has worked well so far; the two stud bolts provide more strength for vertical shear forces from the weight of the mufflers. I have been careful not to tighten the lock-nuts too tight and not over- compress the rubber "sandwich" as the exhaust system needs some flexibility to vibrate with the engine independently of the frame.
This needs to be tight to keep the support, just not too tight. Hope this helps."
All the clearances everywhere are real tight. Make sure you use good clamps between the header and silencer, I found some called 'Moose' clamps, they cylindrical metal pieces the tightening bolt goes through, I replaced the bolt with an Allen head. Putting it together, assemble it all loosly, making sure everything clears, I put a block of wood between the primary case and the lower header and another between the 2 headers to keep clearance there while tightening things. Tighten from the rear to the front with the header roses last, the tightening the lower tube will tend to swing it towards the primary, you don't want that happening.
