The overdrive section is almost bulletproof, but the front section has the same vulnerabilities as the SM318. I have a 67 or so Saginaw that I picked up at a swap meet and the guy didn't know what he had, but it requires tinkering with the linkage. I drove a Borg Warner OD in a 56 Blue Oval from the time I got out of high school. I Hurst Mystery shifter took its toll on input shafts and cluster gears. But it was a fun car to drive. It would paint the street black for half a block in direct with a 3.89 rear and I still have a ticket to prove it would go 120 in OD. My wife drove the car for 9 years getting groceries and hauling kids. She never did have. I have a T89 BW OD which was the toughest one they built. It is out of a Blue Oval, but it could be modified to fit a GM. I swear by overdrives ever since I bought my first one in 1962.