Hi all. Well - looking in the service book there IS a reverse-block valve. I removed the trans pan and moved the manual selector and saw it hit a pin. I poked the pin a few times with a screwdriver and it lowered just a bit. Now the selector goes into all gears. I put new O-rings on the shaft and cable mounts and ordered a new pan gasket. So I lucked out - a relatively E-Z fix. '58 Plymouth - "Christine", '59 DeSoto, '60 Imperial cnvt, '60 Fury cnvt.