I’ve had both units out and they are the same size, the difference between the 2 is the GT headlights has 3 brackets what uses it to hold in place as you know the GTO has a metal bracket that goes all round that is separate from the headlight, so Iall you need to do is grind the 3 small brackets off and the will fit with no issues.
Also I have a GTO so they will fit, how do I know? They are already installed.
Also in relation to your lights, I only take the car out on summer days as most GTO owners do, the lights are for the mot only and it’s the law here to have them on during the day which light magnification won’t matter. The only thing that mattered for me was that the deflection was for the correct side of the road as with the uk lights they drive on the left and in my country the drive on the right (so the uk lights will startle/blind people) hence the need for eu spec.
