Hi Mark. I found a few pics on this website. Scroll down to the targas. It looks like one uses a bolt in bar and the other is weld in.
I put an "Autopower" rollbar in my coupe but had Autopower make the diagonal bar and the horizontal harness bar removable to allow access to the back seat area for stuff. (not for passengers but stuff to take to the track).
http://www.race-cars.com/carsold/porsches.htm
Porsche-o-phile, if you want to install race seats and harnesses, you need a proper roll bar as a minimum to get out on the track (at least with PCA).