So on my 28 truck project I know there is one of the fasteners in the top hinge that goes all the way to through the A pillar, closed cars I imagine are the same.

I don't have either one of those barrel binding bolts or sex bolts or Chicago screws (I've seen a fastener like that called all three)  

There are options on line, but being that I don't know how large the outer slotted head is I don't know what to shop for or even if I can find one.  Also that outside head seems to be rather low domed like say less than a standard carriage bolt head.  The inside screw I believe is just a flat head counter sunk cap screw maybe 1/4 20 threads.  

Any info anyone can give me on the fastener or where to track one down would be appreciated.  Maybe someone has a pair available which would be great because I prefer to have original parts.

Thanks!