Flat head Ford transmissions in general, were pretty weak sisters, as transmissions go. Back in 66 or 67, I had a friend John Donald who owned a very mildly modified 53 Ford sedan with the original flathead. One summer John and I used up every transmission out of every wrecking yard in a 50 mile radius of Stirling, Ontario. We got so good at changing transmissions in my dads driveway, that by the end of the summer we could change one in about 20 minutes.
That was in the "heyday" of midnight drags, power shifting, cruising the drive-ins, and "chirping the tires on a shift into second gear" on the main drag, if you knew the town cop Charlie Bang Bang was busy at the other end if town.
Finally, John got rid of the car because it was becoming impossible to find a transmission within a one hour drive of home!!!!