I'm planning on building my 2wd 59 longbed 3200 into a 4x4. I've been told that there may be a difference in the frame between the 2wd and 4wd models during this year, is this true?

I know I can use any axle and I can even change rolling chassis' up to the mid 60's and my body should bolt on. But this is supposed to be a project. With that in mind, I'd like to keep it all original equipment for a true to form 59 4x4 and not some late model pickup with a 59 body on it.

any help would be appreciated
Thanks

59 Fleetside Longbed-350 Crate
76 Jeep J20 Ambulance
2007 Wrangler X