like these

good or bad for fitting to cast iron head?

(they are UNC allthe way, standard ones are unc/unf)

I would stay well away from them as they get hot and cold all the time, i would think the thread would pick up and a good chance of snapping. (Stainless when heated will expand, but when it cools it contracts more than its expanded) Hope this makes sense.

Put it this way I bought a cat silencer pipe for my Elise and it came with stainless bolts. I used them but a week later I had to remove the cat bypass for an emmissions test and all the bolts bar a couple sheared off! I learnt from that experience.