It is very possible that ChryslerCorp subcontracted the frames to International, especialy if International had extra capacity. I recently spent an hour talking to a retired AO Smith welder who made frames for most GM cars including Corvettes. He did have tales to tell. For example, every year the AO Smith guys would put a Chrysler on a full perimeter frame and give the Chrysler brass a ride, showing how much better it rode and how much quieter with the full frame, but ChryCo stuck to the unibody. Or, how, the tabs for the IFS on chevelles, etc, would get bent going down the line and had to be hammered back into line by the guys who put on the front suspension. That until someone invented the hydropierce machinery that punched the holes at the end of the line!

Remember, too, that a major US auto manufacturer had John Deere make blocks when the original manufacturer was short on capacity.

Why change frame manufacturers in the middle of a body style? $2.99 lower price per frame!

R.