Moving chainplates on any boat, can create more problems, and be much more time and money consuming than first thought..... Easier i feel, to match the mast to the boat, and as by the sounds of it you have lots of experience working with alloy machines, fabricating new spreader sockets, stay points etc should be a doddle.
Worth looking at the construction of the spreaders, if they are just a piece of round tube, then it my be worth changing to a foil section if the spreaders are well swept, as this is more suitable for the higher loads etc, and more straightforward to get a strong attachment to the mast
Rob