One of the guys at Rocket Motorcycle in Toronto (20 years ago - I don't know if they're still around) was very good at welding up and redirecting headers and exhaust cans. What about seeing if someone could be creative with the Kerker you picked up? Another alternative is finding a different header at a wrecker and grafting on the Kerker can.
As for the Mac pipes, I paid $299 Cdn for mine. The oil drain plug and filter are accessible. It bolted on in about half an hour, and took another half hour of fiddling to solve the air leaks. It hung a little low and wide on the right, so I used the armstrong method to bend it up and in a little. Now it sits just under the passenger footpeg, almost tight against the axle bolt. The Mac isn't pretty, and sounds like two Briggs & Strattons nailed together, but it does the job. I reset the carbs to stock jetting and things run fairly smoothly.
Try the links on the Mac page
www.macperformance.com/store/category.cf..._ID=626&CatLevel=top
Here's a last alternative; call Mac and order the header, which exits to the right and won't interfere with the monoshock linkage, and graft on the Kerker can.