O'DAY did some funny things after creating the DS II, Javelin II and Widgeon II........ Those are the "second generation" versions of those boats, only the DS II retained the designation for very long (maybe because the DSA made such a stink about not being consulted about the changes and insisting that O'DAY continue building the DS I as well as the DS II) but anyway back to the question at hand. On the earlier, 1963-70 Widgeons that fiberglass, box-beam that the mast step sits on joined the forward flotation chamber to the forward end of the CB trunk and was also glassed along it's edges where they met the bilge. That pretty much locked it in place and the work was done right because, well... you could see it and it was a very visible part of the boat. On my DS II this same box beam exists, but it runs from the remnants of the molded forward flotation chamber to just forward of the mast step location. The mast step is supported by a plastic pipe between the underside of the cuddy floor and the bottom of the boat. The box beam sort of floats ahead of this loosely secured by fiberglass tape just like this Widgeon. In reality the beam serves little purpose on the DS II, really just keeping a partial bulkhead in place under the cuddy floor which keeps the chunks of foam contained forward of the forward bulkhead in the bow.
OH yeah, back to the Widgeon, looks like a Monday morning or Friday afternoon boat! Box beam is hollow fiberglass beam, glassed in place in bilge. If your mast is fairly well centered, is: not leaning to one side or the other.... I'd try to secure it In place with thickened epoxy resin, possibly insert some kind of solid bock (epoxy-coated wood?) bracing the box-beam against the foam aft of it (or is that forward?) as long as the foam is solidly fixed. If mast is leaning to one side or the other, carefully unscrew the mast step from the beam (after beam is locked in place) then carefully re-step mast, adjust so mast stands plumb. Now trace around mast step and then unstep mast and resecure mast step In the new position (new holes will be needed and the old ones filled in most likely). This procedure is (believe it or not?) pretty much what O'DAY suggested in the original Rigging guide! I guess maybe this mis-alignment wasn't as uncommon as we would surely wish it was!
I'm still curious as to what Rudy may say about this photo....... hope he has some good advice. The Widgeons that he had built (1990-2005) had a different mast step setup.