Thinking about converting from 4speed to 904 or slant six 727.

I rebuilt my first 727 in 1985. I did a reverse valve body mod, that 383 would smoke some rubber and it was a pretty quick car. That lasted a year and it locked up on me cruising at 40 mph. I thought the 4:10 diff locked up until I looked under the car and saw bellhousing pieces on the ground. And a big splotch of fluid. I did another after that but sold the car a few years after. And pretty much gave up owning a muscle car. 28 years later I picked up a 66 dart with a slant and 833od.

It's a fun car, but I'm older and really have been thinking about getting into automatics again. I dont want to get rid of the car, just considering going automatic.
Thanks for your knowledge.