You could get away without some of the electrical stuff... it's designed to kick down into normal drive when you floor the gas. But it wouldn't be too hard to adapt a common relay and a momentary contact floor switch (starter? horn?) if you don't have the originals. If you need the lockout cable assembly, those may still be available from Ford truck specialists. (I bought one around 1990, although the plastic handle looked like a different type of plastic than would have been used originally.) I only took one test drive with the O/D transmission, since something went wrong when I reassembled it and the cases didn't seal properly. That particular transmission wasn't from a Ford, and has since gone to the scrapyard. (I did save the solenoid and governor.) I scored an allegedly Ford 3 speed/OD from a swap meet, but haven't tested it out yet.

For a working truck, it might be wiser to install a truck 4-speed (with the granny 1st gear), or spend the bucks for a modified bellhousing to fit a modern overdrive transmission. I've encountered a couple of hills that couldn't be climbed with a loaded truck in 1st gear with a light-duty 3-speed. One hill could be avoided; the other I backed up and took a run at.