I don't think it will fit one that had say a Westy rear hinge roof previously - or one with a full length sunroof.
I'd imagine the hole has got to be the right size in the right place: crossmember behind the cab and above the rear seat.
Would say that's about right not long got it and it's at mates getting welded forgot what looks like.
I think rear hinge Westies have the biggest hole, and they had a steel crossmember above the B pillar, and another immediately behind the rear of the sliding door (C pillar)...and a third at the rear of the rear windows. If your sunroof is this big, maybe a Westy roof would be better for you?