It's been a long time since I've done any engine changing on these cars but I seem to remember some thing being different about the crank on the early engines. I'm thinking the crank register where the torque converter goes is smaller on early engines that it is on later engines.
I'm not sure when they made this change but you might need to check it out before you buy an engine you might not be able to use.
That being said I have several rebuildable engines to choose from but the oldest one I have is a '68 so I'm not sure I have one that will work. Price range from free to $100.
I'm located in south central MO at 65557.
Dallas