Ok so I figured out the problem, it turned out when I fitted the pump the pin on the rack wasn't engaged correctly with the governor mechanism, it turned out that I simply needed to turn the lever highlighted in the attached photo fully clockwise while putting the pump in position for the pin to engage in the correct place.
View attachment 101536
The generator is running fine now and even running a bit cleaner and quieter than it had before the old pump failed.
As regards the timing shims under the pump, when I removed the pump this time around i discovered that there is a steel shim under the fiber gasket fitted to my engine, I suspect someone had the pump off previously and possibly lost some of the shims and replaced them with a home made fiber gasket, so just in case i checked the spill timing and it's accurate, I may replace the fiber gasket with the correct shims at some point but it's ok for the moment, at least the generator is running again.
Thanks for the suggestions.