Swing-D, it might be a bit more complicated than that, but you're basically correct. Things like the correct flywheel, engine mounts, etc. would have to be purchased or fabricated, but the old hydro was pretty adaptable. Finding one of those Chevy V-8 to Hydramatic bellhousings might be a challenge, as they weren't too plentiful when they were original equipment, and 50+ years have taken their toll on their numbers.
The term "Dual Range" actually applied to transmissions built in the 53-55 model years or so, when GM added a "Drive right" or "Super" shift lever position which prevented the 3-4 upshift from happening until about 65 MPH. It was intended to give better throttle response in traffic, etc. Earlier Hydramatics had a shift quadrant that included only neutral, drive, low, and reverse positions. Park was accomplished by placing the shift lever in reverse with the engine off, and a locking pin would engage the output shaft, locking the driveshaft. Transmission oil pressure would release the pin when Reverse was selected with the engine running, providing a reverse gear.
In 1956 the Controlled-Coupling Hydramatic was introduced, with a revised shift quadrant consisting of Park, Reverse, Neutral, Drive, Super, and Lo positions. This same basic shift quadrant was used through the Turbo 400, 350, and some other applications with various changes for some vehicles.
Jerry
