My 82 KZ550 ltd currently has a single front disk which has had it.
that got me thinking about a twin disk conversion.
I have the chance to get a kz1100 wheel with disks for a reasonable price but would it fit? Or are the forks wider on dual disk forks?
If it would fit, my forks have caliper mounts on both legs. So other than a caliper, would it be a splitter and mastercylinder to convert over?
You might want to take a close look at your front wheel. It may already have the mounting provision for the extra disc.
Regarding the caliper, you will have to find one with the proper hanger. Frankly, I'm not sure if it exists. Hopefully someone here will have a better answer.
For a master, you will want one with a 5/8" bore. For lines, you can skip the splitter, and simply run two full length lines. On, some modern bikes, one line runs to one of the calipers, then a second line jumps over the wheel to the other caliper.
On EB I'm seeing 1100 wheels that are 19 X 1.85 which is the same as the 550Ltd, so it may fit fine. My neighbor put a KZ1000 Fr wheel on his KZ650-CSR. the csr has the same size wheel as a 550Ltd. I think the 1000 wheel he installed was a 19 x 2.15. The speedo drive gearbox didn't fit right, so he had to rig the speedo cable but I forget exactly what he did.
Guessing on a brake caliper, but probably a KZ550-D1 GPz or KZ750H Ltd >> from the diagrams these models have the same calipers. also the 1000K/M Ltd/CSR models. Guessing on the fitment because the GPz550 has the same steering stem as the 550Ltd. also, you may need to swap out the LH brake pads w dual disk brake pads.
Another consideration is that the dual brake disk rotors can be smaller than single disk. If your forks will accept a RH caliper, you may need to get a second 550Ltd disk. measure yours beforehand and get the measurements of a donor disk.