Ok, I'm looking at my factory assembly manual that covers 1947 -1954 Chevrolet Trucks and although it does not show the outside measurement for the outside bolt as you requested, it does show that the distance of the single bottom bolt to the truck centerline is 29.460" ( Sect 1, sheet 1.07 ) so from lower bolt to lower bolt would be 2x or 58.920". I cannot verify but it appears that the bottom bolt hole is "centered" between the two upper bolts on the lower hinge. Just in case you need it, on the top hinge, the single bolt centerline is 28.460" . Hope this helps.
Last edited by Dusty53; 01/05/2018 8:09 PM.