Those "pins" are nylon. Factory installed has grooves machined in caps abd yokes. After assembly, liquified nylon is forced in one side and out the other and allowed to cool. When replacing ujoints, new ones will have "C clips" that lock against machined surfaces on inside of yokes.
The reason for having to pry out the rear yoke is that the rear end moves forward, in relation to the transmission, when it drops down. You can see this if you will take and move the rearend into normal position while the car is raised.