Welcome to the forum. You should get up from your chair right now and go pay for that sedan...........it looks pretty solid and well worth building.
I'll let the Mopar guys and others steer you on the ins and outs of doing one of these, but I have to say, you are the first person who has come on here with an honest appraisal of your skills and ability to complete a project. Most people come on with all these hopes and dreams, and nothing to back it up. You have taken a realistic look at your ability to actually get this car on the road, and that is cool that you are able to do this objectively.
If it were me in those circumstances, I would buy the car, but go easy on it at first. I would clean it up underneath and rebuild the stock suspension and mechanicals, and then get it running if possible. Later Chrysler engines are out there that will adapt pretty easily I think (the flathead 6 cylinder variety) and would allow you to enjoy the car while learning and planning the next steps.
I love the looks of this car, and if you can pick it up as cheap as you say, it makes it even more attractive. Just make sure it has a title or that one can be gotten before you lay out any money for the car or on fixing it up.
Good luck,
Don
A belated Happy 78th Birthday Roger Spears
Belated Happy Birthday