Hi Simon
Have you thought about asking Gosport Boatyard to have a look at it. There are not many things they cannot sort out and they do have access to a very good stainless steel fabricator.
Is it not possible to access the bolts via the anchor locker even if it means hanging upside down. Failing that could you attach a suitable stanchion foot to the deck and insert the pulpit into it.
Hope you get it fixed
Andrew