I also have a '62 C10, which I am also considering going to an automatic trans. Just some thoughts:
1. The six you have in there now has two motor mount supports in the back for the three speed bell housing, and one in the front of the engine. The automatic has only one center mount.
2. The automatic must clear the torsion bar support in the back and and also line up so the drive shaft can go thru the center of the X frame.
3. The floor board cover will have to be modified.
4. If you use a floor shift, it must be able to clear the front of the seat.
