Pull the transmission and reseal it and install a new pan gasket. For the cost of parts & labor, to convert from an automatic to a manual (done properly & workmanlike), you can rebuild the factory-correct Powerglide and retain the originality of the truck.
I have converted several from manual to automatic, at the truck owner's request, but never had a request to convert a factory automatic to a manual. When doing so, the cross member, column, shift method & drive shaft must be changed...if the conversion is done to maintain the equity or originality of the truck. There were far fewer automatics put in these trucks, as compared to 3-speed and 4-speed manual transmissions, so finding an original, that hasn't been molested, with the original 2-speed Powerglide automatic, is hard to find.
