The mount points are the same. The OD units have a rear mount extended so that it fit the existing truck mount points, while taking up the additional length and fitting the existing transmission mount points. It's a simple bolt in swap. You will also need a driveshaft about 4 inches shorter. You will also need to provide 12V power to the transmission to activate the overdrive and lock up the converter. A simple single toggle switch will accomplish this. You can leavve the switch on and the transmission will shift into OD shortly after 3rd gear, and the converter will lock up right after OD goes in. It can get tedious flipping that switch if you're in a situation where OD + lockup is too much for the speed you're going. Where 3rd gear is ideal, you have to turn the OD power off. A more "automatic" method will accomplish this at some cost. Go here:
Scroll down to Dodge 518 conversion. It's gonna be the same deal for the 500.
Your mechanical linkage will swap directly.