Well 48, you're probably right. I don't know from experience, just from what I've read. I do know (from experience)
they started using the "ladder" frame in 63 which was a switch from the "X" drop-frame used from 60 to 62. What I read was that the same "ladder" frame was used from 63 to 87 on light duty trucks. I will search my literature for the reference.
