These old O/D units are "scarce as hens teeth" as I've heard it put. Replacement parts, like the governor, and the solenoid that make the whole thing work are not to be had new. So you gotta take your chances when you find one. I got lucky and found one in an online classified. There are two types, the older "Muncie" style (54-66) and the newer "Saginaw" style (66-87). Basically the same tranny as the stock unit with a BorgWarner "R10H" tail end that held the overdrive. These were placed mainly in business type vehicles, rarely in trucks, quite a bit in station wagons, and "Checker" cabs. Excellent info on this tranny at www.speedprint.com/Deves50/OverdriveIndex.html