My '68
Caravel had cast aluminum BAL style jacks only on the back. My experienced shop didn't think they were original in '68, but I'm not sure about that, and don't care. They worked, and I was even able to change tires with them. I've used the screw type jack, and I think you'd have to weld a little 1" piece of 2" black pipe vertically to the bumper extension and the A-frame to keep them from falling off the jacks. I replaced my frame and the cast aluminum jacks weren't on the new frame when I picked it up to finish the trailer, and I think it's important enough, I'm making a 500 mile each way trip to pick them up and have my machinist buddy rebuild them/hard chrome plate the Acme threads. I'll probably weld the piece of vertical pipe on the A-frame, to keep the belly clean up front. Jerry