frank1492 wrote:

There is a stainless steel bolt ... ("growed" in)...

Sounds like a case of stainless galling, perhaps. SS is notorious for
that if overtorqued w/o a lube.

Others have suggested I can only support directed heat at the shaft
around the bolt shaft, assuming you can get to it. Alternatively, you
might try putting the whole thing in the deep freeze overnight and see
if the differential thermal expansion will help. Applying heat while
cold may help, but you'll need more than propane to do any good, I
suspect. The cat's meow would have been to use an impact driver while
you still had the head, but that's over with now...