As far as my books tell me you will only have to change the torque convertor, the rest of the conversion should be bolt and go.
You will however want to make sure.
First look at the trans-to-engine bolts, they should be directly in line with each other above and below the locating pins.
If the two bolts directly above the pins are closer toward the center of the engine it has the Buick-Olds-Pontiac-Cadillac pattern which I highly doubt.
Next, the motor mounts may have to be moved to line up with the new engine, but that is a unbolt-move-and re tighten step.
You will have to purge the fuel system of the diesel fuel, as much as possible. A gallon of diesel in a 20 gallon tank of gas won't hurt anything unless you have to pass a sniffer test.
Your high capacity cooling system for the diesel engine will work without any problem.
Your engine wiring harness will have to be changed to match the corresponding gas engine but that should be easy enough.