I'm not familiar with that Puddleduck. There is another Puddleduck that I'm aware of, a simple 8', usually home-built dinghy
-- but it sounds different from what you have described.
As for the rig
/mast: Your description of the sailing rig
, foils, and hardware all sound very similar to the two-part fixed gunter rig
used by Dyer on their smaller 8 and 9' dinghies
(The Midget and Dhow, respectively). The Dyer spars are made from spruce, but the rudder foils are varnished mahogany, I believe.
The 9' Dyer Dhow also had a stayed, single-part aluminum mast option, in lieu of the standard unstayed gunter rig
(or maybe the aluminum was standard and the gunter was optional -- can't remember anymore). Which is why I thought of the Dyers when you mentioned the second aluminum mast.
But the Dyer boats were not sloop-rigged. They are more like cat-rigged, with a single mainsail stepped forward in the bows.
So I guess it's still a mystery -- although Caleb sounds like he's on to something.