Your 7th digit in the VIN is a 4. That is the engine code that means L32 which was only in the GTP. If it was a top-swapped GT it would show a 2.
There is little difference b/w the GT and the GTP, you could de-option the GTP also.
The PO may have changed the badge to avoid the unwanted attention a supercharged car gets.
Here is a link that shows how to install a boost gauge.
Boost Gauge Install