You are better off buying GSXR1000K1 calipers in the USA. The climate there is much better, and generally the inner faces of the caliper body and pistons and seals are in much better condition than on a brake donated by a machine from the UK of comparable age. eBay is great for this and you should be able to get a pair of these braces for between $75 and $150 depending on the seller. You will almost certainly need to clean them prior to installation, but once the brake dust is removed, an American-sourced caliper will likely always be in better mechanical condition.

The original hose arrangement on the ZZR1100 consisted of a single hose from the master cylinder reservoir to a union mounted on the lower yoke. This then split the fluid path into separate hoses for each front caliper. There are small performance losses through this arrangement and the best way to install your new brakes is to replace the hoses with two single lines emanating from the master cylinder from a double banjo bolt, directly to each caliper. Braided hoses will also improve the mechanical efficiency of the setup and do more justice to your new installation.

The aforementioned procedures represent an update to the original configuration. However, they are not required and you can use your entire existing system as is, with the GSXR1000K1 calipers, if you are on a tighter budget. Whichever route you choose, you need to remove the OEM four-piston calipers from both hoses. Once you are ready to install the replacement six-piston units, you must install an adapter sleeve into each caliper mounting hole in the fork legs. The sleeve requires reducing the inner diameter of the fork mount from 10mm to 8mm to take a bolt to fit the female threads on the stock GSXR caliper. These calipers also require 1.5 to 2mm of shim to properly align with the brake disc and a flanged adapter sleeve can also perform this function. An alternative to the sleeve is to use a 10mm shoulder bolt with an 8mm thread and a washer to align the centerline of the caliper. This is a less aesthetically pleasing solution and a bit more complicated to install.

With the adapter sleeves in place, you can move the caliper closer to the fork and bolt it using two M8x40 bolts through the forks and sleeves into each caliper (torque specified for OEM installation). All that remains is to connect the existing or replacement hoses to the clamps and bleed the system. There is a short information page and installation video on this that may be helpful.

Happy braking.