Dear Martin
We had the mast down on Delphine at the beginning of the season, and the guy, Rob, who works on her for us encountered a similar problem. I've asked him what he did and received the following reply (my italics so that it's clear which bit is Rob's advice):
The nuts are either encapsulated or underneath,I forced the foot up to put some weight on the nuts and cause friction,
I then managed to slowly turn the bolts,
Fitting a new step will be tricky as the footprint might be different,
They will have to have some fibreglass work done to accommodate,
We bonded an aluminium plate in and I drilled and tapped to fit new step,
This is the only way I think,
They could drill the heads of the bolts off to remove,
Regards
Rob
Rob made a super job of it, including getting a specialist fibreglass repairer in to finish off where the existing fibreglass beneath and around the mast area was crazed. I think our system is now as strong as or stronger than the original because of the addition of the aluminium plate - but if the fibreglass doesn't look damaged, the solution proposed by Chris' boatyard could work if the holes on the new step line up with the original ones.
Good luck with Ariel
Gilliane
Delphine, Parker 275, no. 41