The 1100 Swinging arm fits straight into a mono frame but is a different width to the paralever swinging arm. You have to weld a small spacer to the left hand side of the paralever frame to take up the slack. and then tap through with a 20mm 1.5 tap to keep the support for the swinging arm pivot.
The offset on the rear wheel is approximately 20mm which is where the 20mm figure mentioned above comes from.
I was putting this together a couple of years ago. You can see the offset using unmodified standard parts. The 1100 swinging arm is considerably longer than the standard paralever one. If you fit the 1150 swinging arm it's only slightly longer than the paralever setup.
Getting the wheel pulled into line is the hardest part, everything else is pretty straight forward and deceptively easy. Though you will need to make a decent bracket for the top shock mount. You end up with a very high machine that I thought was very unwieldy. I sat on one of the bikes crazy Ivan had built and it made my 1150 GSA feel like a toy which defeated the object of having an airhead. You may as well run a stripped down 1100GS