The 904 is just that an automatic 3 speed.... when Mopar dropped the slant six the rest of the A904 variants and the OD upgraded version the A500 all were for the LA bolt pattern (318/360, etc...)... The most common ways to get an AOD into the car are:

Mopar 60's truck adaptor plate that goes from slant to 318, this will allow the A500 to be installed, but takes some other mods ot your cross member and the floor tunnel since the A500 has a wider rear section than the A904/A727... (there are some people that have done this mod and posts are on the board).

Version 2 also needs an manufactured adapter plate, but allows the use of the GM 700R4 transmission, there are a few that have done this as well....

The last version is not so common, but at least one person has done it... a bolt on OD that couples with the output shaft where your driveline yoke is installed at the end of the tranny... the kit is $$$ and a few more mods as well...

This same style of bolt on OD was used by Volvo in some of their cars, but again, some $$$ to machine an adapter and time to figure out how it is going to install...