The AllPar tech article I posted a link to has a lot of historical info as well as theory of operation. It also discusses similarities and differences between the various Torquflite models. Worth a read for sure. And it does tend to confirm the 904 guts in a 727 case...
The 998 was a 904 built inside a 727 case. AMC used the same transmission case behind all its V8s but only used 727 internals behind the 401.