eBay 4 million reasons you'll find it here
 
    The tricky part:  The latching rail and pin needs to have a home for the seats to adjust and lock in place.  These were welded up one afternoon er-week out of various pieces of flat stock, angle iron, and tubing - hail hail the wire-feed welder!
 
    Here it is all dressed up & perty.  The white squares are nylon nut-serts for the seat rail to slide on. The rail has a row of holes in it and a rod that runs through the U-shaped thingy with the spring attached.  You pull on the handle attached to the rod, it moves the pin out of the hole and allows the seat to slide forward and back.  When you're done you let the handle go and the spring pulls the pin back into the hole.
Yes, we had to make three of these to get two usable models.
 
    Tracks and front adjustment pin confabulation thingy bolted in.
    You can clearly see that the floor has completely rusted away and been replaced by what looks to us like a piece of trailer roof!