I'm going to flatten the top of the two rails, screw steel bars to them (producing a lip on the outsides of them) and make a carriage to ride on there. Plus a leadscrew to thread it back and forth. Step one in the development of a metal-cutting lathe...(Gingery-free(!!!))
You can see the basic arrangement, pattern diagonally in 10x10x3" cast aluminum flask with sprue and riser pegs at either end. It looks dusty because it is, I just applied parting dust (wood and paper ashes work nice!).
Done ramming the cope, now carving away the sand (coping out) to the parting line. Here it's 1/4" from the bottom of the base plate, thus leaving the plate in the drag and the bars in the cope.
Cope and drag are finished (drag is sitting nearby, ready to accept its load). This is the cope with pattern pulled.
D'OH! I forgot the extra pound of metal. All that extra slag on the melt must've tricked me out. If it had the full pour there would've been no shrinkage on the rails, only in the riser and sprue where it's supposed to be. So I'll have to make another one.