I know I'll be going down as a minority on this one being a a-body site. I voted the 55 dodge for a few reasons.
1- your dad already has and likes this car? Perhaps the two of you could work together on it and it become an important part of your family for generations to come. These family projects are the best cars to own if you get the chance to follow thru with them.
2- I like the gasser as done back in the day idea mentioned by Bruce.
3- You can always get a notch later.
Me and my father worked together on a 56 but he lost interest a decade ago.
The project sadly sits stale now. I always wished we started on the car when we were a little younger and got to finish it together. Your poll just reminded me I need to do something with the car.
50s mopars are some great cars. All the best on your next Mopar which ever you choose.