Thanks guys.
So running plates now fitted:
http://www.flickr.com/photos/33105452@N05/4305915833/
For future reference, the procedure I used was:
1. Test fit bar, filing out rear wheel arch where necessary. I set it so that the plate sits on top of the suspension mounting lug, just resting on the bar.
2. Drill and rivnut the 3 M6 fixing holes. Attach bar.
3. Test fit plate (straightening it out if necessary, both mine were curved despite the flange), cut back the flange where it interferes with the suspension lug and exhaust mounting bolts. (Power file was great here!)
4. Drill 4 M5 holes in the flange (allow enough space to get a screwdriver to the front one once its in place). Mark these holes on the chassis.
5. Remove bar.
6. Drill holes and rivnut the 4 mounting points for the plate.
7. Reattach bar. Attach plate.
8. Mark where you need to trim the plate.
9. Remove plate. Trim. Refit.
10. Work out how to attach the bar to the plate. I haven't done this yet as the plate sits pretty much on the bar anyway.
Total time: Well the second one took 3 hours and was much quicker
