I've got an old GME Gooseneck frame with the plunger suspension on the back. The frame is pretty rough, but if I ever get around to doing anything with it, I'm gonna put a hardtail on it. If anyone's interested in the plungers, I'll post them when I "cut it up".
Come to think of it, I'm pretty sure I've got the rear suspension off an old Indian out in a storage shed. A buddy of mine cut up the frame to build a three wheeler back in the 70's. I hauled of his junk. (G)