I have a set of aftermarket (Folger) trubo +1" width rear flares. I imagine they were added in the 80's, no cracks or showings of cracks, but these were definately made for a street car. They are very thick. This could be because the car was in a very mild climate, stored in a garage and has only had about 20,000 miles put on the car since 94.

For the money I would go steel. I am putting flares on my 914 and am going with steel simply for the fact that if I am going to spend big bucks on a bare metal paint job then why skimp on something that could ruin the whole thing in a relatively short period of time (assuming its a dd car).

That looks like Porsche SINGER type clone?

I wouldn't bond FG to steel but as others have said I would go full FG fenders. I currently have steel flares in the back and FG fenders up front. I used rubber paint on the inside of them prior to install. This will be my second time running full FG fenders in the front. Ive never had a chip or crack with the last set which I ran for over 10 years. Backdate project is the only reason Ive changed them.

I have riveted SC flairs on my 77S, done by a PO, not certain how long ago. Held up nicely so far.. In some lighting I can see the rivets, and someday I´ll probably go back to steel.

However, when I last fall was getting the car road safety approved, Porsche Norway, would not give documentation of anything but welded steel being OK. Due to structural integrity issues, was what I was told. Not that I´m worried and I got my car approved without problems.