[Walt Fricke]

These are the extra stiffeners Porsche put into its Targas, and later into its Cabriolets.

The longitudinals under the doors have one extra layer of sheet metal included in the sandwich. And the A pillar/windshield frame have one extra layer. And the tire well covers (wheel housings) on both the passenger and driver's side have an extra layer of sheet metal (which is why you need different or trimmed aftermarket floor boards if you add those as replacements).

Plus a look at a catalog shows a variety of stamped parts which are listed as for the Targa.

I believe the Cabs (which came later, with the 3.2 Carreras?) have similar reinforcement.

And the Targas, at least early ones like a '68, have welded in mounts below the dash, and a bolt-in bar (cross tube in the catalogs) running from side to side.

Still, these cars have lower torsional rigidity that the coupes. There is a long discussion on this list from a few years ago by a guy who wanted to stiffen his Targa, but not have more than, I think, a welded in roll bar. Lots of ingenious stuff.