I believe the 4-speed Hydra-Matic was the only automatic transmission option in 58, and it's a huge job to convert to a standard transmission. Be sure to save all the automatic-specific parts you take off, as there are plenty of people wanting to go the other way and those parts are very scarce. Unless you plan to do a butcher job with a floor shifter, you're going to need a different steering column, shift linkage, clutch pedal, and possibly the crossmember under the bellhousing, bellhousing, flywheel, clutch, pressure plate, shift linkage, etc.
It would be best to try to find a complete donor truck with a trashed-out body to be sure to get all the bits and pieces you'll need, or just try to find a stick shift truck in running condition, and sell the automatic truck.
Jerry
