I should add that my high oil pressure issue seems to have resolved itself. I removed and reinstalled the oil pressure relief valve plunger and since then I' ve had a steady 40psi cruising and 10-15 at warm idle. Hopefully a once off glitch that won't repeat itself.
I've updated this thread to replace the deleted photos which disappeared when my service provider reneged on their 'free webhosting for life' promise. It was useful to look back over as I'll be doing this again soon. This time I'll be making use of plug and bottoming taps also to try and reduce the depth of the tapping necessary to sink the plugs. I'm sure I'll report back...