The 1st trans was probably the one that came with the motor, after that, they were all rebuilt. I discovered how cheap it was to rebuild a 904 or a 727.
The torque converters were also either new or remans. I'm sure the clutches and plates were OK, but everything inside the transmissions was covered with the insides of the torque converters. It was more time consuming to clean up the mess then it was to throw a rebuild kit into a clean trans. I could buy rebuilder 904s for $25 or 727s for $40 each, and the replacement torque converters were $25 each then. Good used trans were $150-$175.
I suppose, rather then blame the 904, the blame probably lies in the torque converter hubs or the front pump. When you install them both new, and less that a year later pull it out to find another cracked hub its pretty hard to figure out which caused the problem.

You also need to know I was pretty hard on everything I drove back in those days. I didn't need the hot rod to run in order to get to work, and it showed. I have matured in my driving style since then, some.

The 46RE being installed as a used trans was against my better judgment at the time, my track record with used auto transmissions isn't very good, never has been. But the cost of rebuilding a 46RE (a $600 kit was the cheapest I found) is much higher then rebuilding a 904 or a 727 ($125 kit). I'd gotten to where I was rebuilding those myself, but its been several years since I've rebuilt a trans. The 46 RE has me a bit nervous ripping one of those apart, and inside a welding shop (or at a body shop) wasn't good environments to rebuilt any trans, which were the only options at the 46RE's time. Gene