Pretty sure I came up with 1" also Boss. Not the best solution, I just got a 1" nylon spacer (in one of those drawers at a real hardware store) and a long bolt. There is a weld nut in the radiator channel, which side faces forward is important.
Someone put the radiator on my 64 with no side channels or flat stock on the front and back. I couldn't figure out why the hood was moving so much going down the highway
till I got a good look at it. After the hood was painted I was over the edge trying to get it to fit the Lo Boy..... turns out there is a short run of them with a higher peak and extended radiator neck.
Undocumented, but Tom at TM knew about them. I had a radiator shop extend the neck and will start on the 64 one day soon