This is just hilarious..
Popped a 1/4" bolt in the hole, it's too small of a diameter.. I bought some more 5/16" coarse thread bolts, and tried one in a different hole, it went in about 2 threads and stopped. I know the bolt hole size can't be metric, because cars in 1957 didn't use them. This is the craziest thing ever!
I guess I will proceed with punching new holes, which really bothers me, to be honest. I know I'm not restoring the truck to original, but I like to try to use original holes and connectors when I can. The seats I am installing only match up to one original hole any way, but this is still driving me nuts that I can't solve this mystery!!
