Gearjam, I had your problem with my 1998 XJR, but with one pulled thread on rebuild after overheat. My delema was similar - should I replace all of the theads or maybe the 8 central ones, as these were most likely to have suffered the worst heat damage (anealing?). I could not get suitable 'timeserts' so went for normal screw inserts. I also had to procure a special 'long series' drill and needed to make a special extension to attach to the insert tap.
In the end, I descided to go with just replacing the one pulled as I figured I would still have options if any others failed. Luckily it was successful and I now have a great running car.
However, I had at least one dropped valve insert in each head and I was advised that 0.010" was too much to regrind and so opted to replace the cylinder heads. I would advise that you check your inserts at the least.
Incedentally, I fitted new heads for a 1999 3.2 bought on e-bay for a bargin price. These required that the camshafts, etc be replaced with my own and of course, all of the valve clearances were set correctly. Also, as they were new, the oil gallery inserts were still in place and so suitable for my supercharged engine.

 

Thanks for the warm welcome, I may know my mechanical stuff, but the electronics on these jags scares me. I also should have mentioned to gearjam that he should (and probably has) check the cylinder block faces carefully for any distortion, mine was out by around 0.010" and was 'decked' in addition to a check for porocity.
I have to wonder if there is an approved way of ensuring that the inserts are tight. Maybe the surrounding alloy could be compressed/centre-popped? Does anyone know? I still have the old heads and some of the tools ind inserts for the thread repair - whereabouts are you gearjam?