As long as you don't cut any of the perimeter frame, you should be OK. Make sure you do something to beef up the perimeter, though, and realize that if it takes a side hit, the B-pillar is losing a lot of strength without the roof.
If you can figure out how to install subframe ties underneath the car, that will help give it back some of the strength you're losing.

Yea, subframe connectors would help and are easy to fab.

Since you are leaving the metal around the perimeters, and do a hoop of steel stock around the opening, you probably will not cause any serious issues.

What you are planning...it'* not like carving the whole top off for a targa or convertable...then find out the next day that the doors don't open or close anymore cause the body sagged.

The bracing in the roof is more to support the skin of the roof and the headliner. Yeah, it stregnthens the car by transferring torsion loads across the top of the car, but your new tube around the opening will do that as well to some degree. You are just doing a sunroof...ok, your going to "super-size" it..but it'* still basicly a sun roof.

clm212, I am not following you. Are you agreeing with me?

Yes...If I follow what you have planned, opening up the roof along the red lines in the photo and adding a hoop of steel tube around that opening...then you should not have any problems at all.

Yeah, ok, we are on the same page then. Keep us updated on this project Alex. It sounds very interesting as all of your projects are.

Why is this in Performance?

Moving to Detailing and Appearance.

Well since there is no section for handeling, & my ? is not about looks but about the structure of the car.
& yes I added the hoop to the roof allready, just havnt made the cut yet.

Some pics of the work Ive done so far. Bondo-work is mostly done, but I still havnt made the hole. That will be the last thing Ill do before paint.