Lucky you! No one has given me anything that still moved under its own power, ever.

I would go for the adapter to put the 904 Mopar automatic in your truck. While your changing the transmission, change the rear axle as well. A newer axle assembly with a rear gear in the 3:23- 3:55 range would be a lot nicer behind the flat head 6 and the auto trans, you would be able to drive your truck at highway speeds. Gene