It's amazing what a few hours on the internet can do. I hunted around and found two possible solutions.
The first is another set of pins from a GM car, they are the correct 11/32" oversize diameter and are 4 1/16" long with the correct spline under the head. Cut them to lenght and they should work fine.
The second is a set of bushes from a Chrysler, they have a 1/4" ID and 3/8" OD. I'll be able to ream the hinges to take the bushes and then ream the bushes to take the original size of pin.
Not a lot of money so I have ordered parts for both options, I'll see which will work best and go from there.