I have an 84 GPz1100 arm off the bike buried somewhere and will check in a day or two, but I'm 99% sure it will fit in your KZ1000 as a bolt - in for the pivot width. As far as being a good choice for a mono - shock set up, I'm less convinced. Unless you already have a GPz arm available, including all the shock linkages, axle, chain adjusters, etc. with it, I would look elsewhere. Most Suzuki swing arms up to 2003 have narrower pivot areas than Kawasaki, Honda, and Yamahas do, so installing something like a Bandit 1200 arm typically only require machining spacers (on a lathe) for end play in the KZ frame. Early GSXR arms are plentiful, too. My buddy recently installed a 2000 GSXR-1000 arm in his 81 GPz1100 frame and it was a direct swap, according to him. The Suzuki arms will fit tires as wide as 200 on a 6" wide wheel, and you can use the GSXR light weight wheels and modern brake.
If you do decide to use the GPz arm, I'm again 99% sure the 83 - 85 750 and 83 - 84 1100 are the same part except maybe in small details like the chain guard mounts. I also know that an 88 ZX10 4.5" wide x 18" wheel fits in the arm with little effort (I have one of those, too). It is possible to mount up to a 170 tire width on an 18" wheel, and some 180 tires will fit on a 17" wheel in the GPz arm, again, with some minor modifications. Chain alignment and clearance around the tire and in the frame will be bigger issues to resolve with tires wider than 160 on any KZ1000. Switching to a 530 chain will help.
2-04 R1, 81 CSR1000, 81 LTD1000, 2-83 GPz1100, 3-79CBX, 81 CBX, 3-XS650, 84 Venture, +parts
Quote "speed costs money...how fast do you want to go?" (Which Z movie?)
Universal formula for how many motorcycles one should own = n + 1, where n is how many motorcycles you own right now....