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Here are pictures of the two floorboards. Notice on the standard the floorboard stops at the edge of the firewall. The accelerator pedal is attached to the firewall and there is a hole for the foot starter. The hydramatic floorboard covers part of the firewall and the accelerator is attached to it. There is no hole for the floor starter.
Here are the firewalls. On the standard, the crossmember is one piece riveted to the frame. On the hydramatic it un-bolts. Notice the "hump" cut out of the hydromatic firewall. The neutral safety switch is located on the steering column.
Here is a view of the shifter in the hydramatic. The key switch is different too. It has a start position.
As you can see, the change over to a hydramatic is not just a direct swap. If you want it to look "factory" you'll have a job ahead of you. But it can be done and it doesn't have to look "factory" if you don't want it to. It's your truck.