First, I checked the heads I have and compared the 11mm and 12mm bolts and ability to fit the head. You will not only need to drill for the bolts, but also for the larger washers; unless you use 11mm ones that you drill out to fit the 12mm bolts.
Second, I have two heads, but one that looks to me to be more rebuildable. Unfortunately, I am not a machinist, but it doesn't look to have any water leaks and the cracks between the valves are minimal. It has all but one valve installed, and has the matching cam caps. Also, the prechambers are without any cracks that I can see with a magifying glass and light. $50 plus shipping, with the understanding that I don't know if there are other cracks that I cannot see without taking it to a machine shop. So, it is a bit of a gamble on your part, thus the $50. What is your zip, and I'll try to give you a figure for shipping.
Let me know if you still want to go this route.