Done Injector Timing Advance Plate. Now What?

[jp4294]

Hey guys,
Been having a hot start issue lately on my '99 GU 2.8 and I read up on this amazing plate that advances the injector pump timing. I thought I'd better check it hadn't already been done before buying one and sure enough, the cover has a 4-5mm raised section!
My question:
Is there anything else I can do/look at before I go replacing the entire injector pump with a second hand one?
Is it possible to add a spacer of a few mm as well as the raised cover plate to make up for that wear since the plate was installed?
Any help would be awesome!