Interesting photos.
The first part you must purchase is a service manual for your car. They are available in either hard copy or digital versions, here is one vendor:
https://www.rockauto.com/en/catalog/plymouth,1948,p15+deluxe,3.6l+218cid+l6,1486874,literature,repair+manual,10335
This is a trunion-type universal joint, they are repairable and parts are available but you must have the manual in order to service them. If yours are too far gone to save a new driveshaft can be built that uses modern universal joints but it will set you back a few hundred dollars.