Golden Oldie Olds

This is my first Mopar project and it is going well. It has the 201 CID flathead 6 with s speed. I would like to go with an automatic and get some info on what unit to use. I can get automatic trannys from 57 and 58 Plymouth cars. Will it bolt up and what are the upside and downsides. Any help in direction would be appreciated.

I was really hoping to use something from 54 up for that reason. That block was used clear into the 60's as a power plant engine. That engine was common in most Chryslers, Dodges, Desotos and Plymouths. Just not sure if they will bolt up. I know they used the same style drive shaft and also the same trans mounted E-brake all the way to 1958 which is the same as in my truck. Just hoping to get some info on compatibility. Thanks for your input.

Maybe someone out the has done this or knows if it is possible. My truck has the 201 CID in line 6 cylinder engine with a 3 speed on the floor. I would like to change it over to a automatic tranny. I know this engine was used way up into the 50's. I've got a chance to get a good automatic tranny out of a 1950 Chrysler Windsor with the inline six engine. Question is, can I just bolt this tranny right up to this engine without any adapters or such. I know I will have to come up with mounts and driveshaft, that's not a problem to do. Or, is there a late model tranny that I can use without re-inventing the wheel all over again. Any help would be appreciated