Chris,
I would not wast the time or money to go from PS2 to PS3. You will see no difference.
Replace it with a PS3/2 board if the PS2 is damaged. This might be a tough fit in the Shay tender but you can use all of the existing wiring.
I have always used diesel kits going from protosound to PS2.
One final thought: Shays are an extremely difficult upgrade if you have never done one.
Dave