I also don't think the plate is your real issue. The plate is a "Starter Locater Plate" as defined by Ford. It sets the distance between the starter and the crankshaft. So it is really important.
The torque converter can move in or out more than the thickness of the plate so I don't see that causing an issue. Did the previous tranny fail from overheating or just "old age"? Maybe the cooler isn't up to the job or it's not in the airflow???
Are the cooler lines plumbed into the radiator cooler? I like to go into that first and then into an auxillary cooler. Some guys don't like to use the radiator cooler but I do..... It's your car so you get to decide which way to go.