Wow, that is a work of art!!
By the looks of the work you have don on your 12 you may know the answer to my question....
The two bolts that go into the head just above the two middle exhaust ports, can they be safely drilled out and hellicoiled at 8mm?
Only asking as one of mine has stripped and I am bit worried about drilling it out and taking the edge of a water jacket with it..
Once again, Nice work!