I have installed a z600 twin in my boat and have acquired a manual which may help you although I have never actually removed the pump on mine (and hope I never need to!) It seems to involve lining up the control rack with a groove on the the crankcase otherwise it wont come out, and it may assist you to first remove the injection pump cover - secured by 4 bolts above the lift pump.
The book says as follows:
1. Remove the injection pump mounting screws and nuts.
2. Align the control rack pin with the notch on the crankcase, and remove the injection pump.
3.Remove the injection pump shims
4. In principle, the injection pump should not be disassembled.
When installing the injection pump, insert the control rack pin firmly into the grove of the fork lever
Addition or reduction of one shim delays or advances the injection timing by 1.5 degrees.
Hope that helps. If you want a copy of the manual which has some pictures to assist, let me know at Bobwale50@aol.com