It's not just '75 PR-10s - my experience with Peugeots built about 1973 and later is that they were anything but slack or laid-back. I had a '73 PX-10E, a '74 PX-10LE, and a '75-78 PR-10L. The first two bikes, both 58cm c-c, were VERY upright. I never properly measured the angles, but 74 or 75 degrees sounds about right on them. It should be noted that neither of these bikes had a normal serial number on the BB. The PX-10LE is on First Flight's website, if you wanted to look at pictures.
The 56cm c-c PR-10L seemed to me to be slightly less steep, actually - say 73 degrees parallel. All of them were a far cry from the 72 degree parallel frames described in the various cycling books of the 60s and very early 70s.
My perception is that they got really steep about 1973, and that lasted until 1975-76, when they went to a more conventional geometry - but that's purely my perception.
Russ Fitzgerald
Greenwood, SC
http://internaldetours.blogspot.com