Giles- If you can move the cp's outboard and mount them to the hull, that might be the best thing
I _knew_ there was something I hadn't thought about! Yes, the geometry of NOT moving the lowers closer together makes a lot of sense. The uppers are the pair mounted to a bulkhead, which leaves the option either of cutting a slot in the bulkhead against the hull to allow room for the new cp (and its bolts) or moving it forward/back a couple of inches. The mast is (I think) about 32 ft long, plus a foot or two to the top of the cabin. So the difference would be a couple of inches (if that much, assuming the new cp lay right up against the bulkhead) in 30-something feet. And, of course, it will be the backing plate that butts up against the bulkhead because the cp will be outside. On reflection, it would be best to clear the whole mess of glass cocoon and rotten wood out from where the lowers are mounted, which would leave a flattish inside to the hull to mount a backing plate to. Sorry if this seems a little dense -- it seems as if this task might be the most difficult so far. And why, oh why, didn't I hold out for an M-23?
Cheap it isn't, a GREAT tool it is
On the other hand, clearing the cabinetry out for access to these areas might be a little easier than I'd feared -- Leif Eriksson's praise for the Fein Multimaster Magic Tool leaves me hopeful. Sincere thanks to Jerry and Leif. Giles Morris