Have injectors out, one self extracted due to broken hold down bolt. Extracted the bolt remarkably easily.

New copper heat shield/seal washers have a chamfered outer diameter that faces towards head, genuine parts with helpful diagram to show fitting position.

Not certain as to shape/size of seat. We have various seat cutters, a 17mm flat appears to just clean outer circumference of seat.
Don't want to get carried away until we are sure it should be a flat surface.

A good session on the google has yielded no positive results. Anyone know for sure, or how to find out?

Washer OD 13.8mm. Got a new bigger box of cutters, includes a 14mm flat. Can't see how that could be wrong.

Bottom seat of injector flat?
Does it need cutting, or just cleaning.
14mm will be ok.
(Just a note cutting a seat by hand will never be that accurate) so light cleaning is better.

Just a gentle scrape Keith. Experienced with the process, not done this engine before and didn't have a 14mm cutter/cleaner. Seems a weak design. Any blow by is inside cam cover. Not even a steel sleeve like those dreadful PSA 1.6'S