You can put a K100 exhaust on a 16V engine. I installed a K100 exhaust on a 16V k100RS with no major problems and rode it for over 5,000 miles. It takes a bit of fiddling at the rear mount, but the size and spacing of the exhaust ports on the 1100 engine are the same as on the 100 engine.
The problem with the retrofit is that footpeg plate is a little further from the centerline of the bike on the 1100 vs. the 100. This causes the exhaust to angle out a little and reduces ground clearance when dragging the pegs by being the first thing to drag. I solved the problem by spacing the mount about 1/2" from the back of the footpeg plate. Put everything together on the bike before tightening anything starting from the exhaust ports on the head and working back.