I did this recently on my 65 300. It looks like yours is in a similar condition to what mine was, where the roll pin that held the rollers had sheared off on the inside. It looks like the remnant of the pin is still there (they are hollow--the roller spins on that hollow pin and if they aren't lubricated the pin wears and snaps under the tension of the spring and then the roller falls out). I drove the remnants of the pins out of mine with a punch but then the replacement pins that came with the kit were too small in diameter to fit tightly into the hole in the hinge body, so I had to go to the hardware store to get the right diameter pins. Maybe the pins supplied with the kit were made to fit inside the diameter of the remaining hollow pin bits, but that seems like a dodgy arrangement to me.
Sixpactogo is right about fitting the roller first and then stretching the spring over the lever. Maneuvering the roller into place was a real challenge because it is encased totally by the box-section of the hinge itself, so it is very fiddly and you have to just tickle it into place with your fingertips. Make sure you are in a calm mindset and be prepared to make multiple attempts. I had to use all my Jedi Mind Force to get it in place.
Then stretching the spring was the real nightmare. After trying to pretzel myself into position to actually get some leverage to pull on the spring, I finally fought through the red haze of fury that was descending over my vision, and had the presence of mind to just go ahead and make a tool to hook the spring and lever it into place. I took a large screwdriver and ground a notch on the side of the tip and then bent it at the appropriate point. Basically a tiny crowbar.
If you want I could probably send you this tool I made, because I sure don't ever plan on or want to go through doing that again! If my pain can help others avoid the misery and frustration of installing these springs I would be very happy. But I tell you, the luxury of finally having doors that stay open and not hit you in the leg every dang time or slam shut every time you turn your back was worth it!
(Last photo is after I finally got the jambs painted)