Les -
The slide rod concept can be made "off the shelf" quite easily. The rod should be round, so things will pivot, but the bushing doesn't need to be. The part that does the sliding (what I made the bushing for) can be as simple as two pieces of oak shaped like an "L" that just sits over the rod. Say, an oak 1x2 with a 1x4 attached to it flush on one side. Maybe a shim or two between the assembly and the seat box to give a little clearance for the rod. The most common size of SS rod in marine stores is 7/8", which would be even better than the 3/4" I used because it would be more rigid. Instead of oak, you could use teak, but since you don't see it, oak is cheaper. The rod is the simplest method I could figure out to get the pivot point fully behind the box so the box is completely off the floor when lifted slightly to shift.
Now then, I see what you are saying about making it simple for C-Dory, but I have to disagree a bit. Theirs is a manufacturing plant, for crying out loud! In my mind, the ideal way to build the thing would be the one piece floor board, and a seat box made of fiberglass. The box would have a far greater weight to rigidity ratio if it was one piece construction, including the bottom. I should think that a boat builder would be able to make that, no problem. They could even mold the slide bracket right into it. Done. Simple. Cheap. And they could sell it as a $500 option, no problem.
Now then again - here's an even better idea for the locating tang. Instead of using something that has to be lifted out of a hole and set into another one, how about getting two plastic caster wheels for 39 cents each, and putting them into the front edge of the seat box so they protrude from the bottom 1/4" or so. Then, gouge some rounded depressions in the floor at the two seat box locations. Now all you have to do is release the latch, which I understand is necessary per your explanation, and push the box in the desired direction just hard enough to roll the wheels out of the depressions and over to the next set where they will drop into place. Then you fasten the latch at the new position. Make the depressions deep enough so that the box itself, and not the wheels, is supporting the weight of the box, the stuff stowed inside, and the passenger sitting on it. Minimal effort required, self locating, and no contact while moving other than the wheels.
