904 Transmission Stopped Going Into Gear

Things are definitely strange in this trans, but its the one I got.

My main goal is to use it as a learning experience and get the car back on the road while I plan my v8 swap. I think it will be fine for that purpose.

Another can of worms I need to open is what kind of fluid is recommended for a Torqueflite 904?

I have done a lot of online research and most forums tend to settle on one of the following:

-Dex III
-Type F
-ATF 4+

Most forums also contain a lot of heated debate about which of these is best.

Anyone have any thoughts?