OK, just spoken to a Isuzu mechanic at the Isuzu main dealer for Exeter and he has checked on his system and can confirm that they are not stretch bolts on the 3.2.
In his dealer manual (which he won't let me have a copy of ) it says to inspect the bolts for signs of wear and replace if necessary. He also said that they have only ever done a hand full of 3.2 head gaskets but can't remember ever needing to replace the head bolts on any of them.

I'm guessing they only needed to move over to stretch bolts when they increased the engine size from 3.2 to 3.5

If I do need any he can order some in and post them out to me at £7.59 + vat each!