Earlier boats - 60's and 70's - often had sliding goose necks. This was part of the main sail shaping process and there was a small tackle under that 'slider' that allowed the main to be pulled downwards to tighten the luff. Somewhat later, depending on model and make, fixed goose necks came into common usage. screwed or riveted to the mast below the slot. This change was driven by racing rules, trying to keep owners from cheating and their main sail area, and also by being a bit less expensive for the builder and also easier for the owners to deal with.
(Just my opinion, YMMV)
I would guess than most owners of 'classic' sail boats long ago converted to a fixed from a sliding goose neck. (About the time that roller furling booms went away...)
Which type of goose neck does your boat have? Can you put up some pictures??
A replacement will need to fit the mast contour solidly, and also fit inside your particular boom extrusion. Finding an exact fit gets interesting when a boat is 30 or 40+ years old. The better news is that thousands of similar boats were sold.
On the plus side, making a smaller "double pivot" piece for a lighter-loaded boom on a 27 footer should be pretty easy for a small machine shop. Material is minimal, but labor will be a factor.
Search Engines like google should help you find a new one that can be adapted to your spar section.
Hopefully other owners of similar size boats will have specific suggestions.
Added link to an earlier thread with some pix.
http://www.ericsonyachts.org/infoexchange/showthread.php?3347-Old-E27-Gooseneck-and-Boom
