A quick look with Google revealed the following:

http://www.carfolio.com/specificatio...car/?car=71588

and

http://www.automobile-catalog.com/ma...gt_j/1971.html

Don't have a clue where those two websites came up with the numbers, but assuming it was copied from something official, the early high CR (9.5:1) motor apparently had 89 DIN hp. I also found references to "90 PS" for that motor in European Opel forums, etc.

So our (USA) 102 SAE gross hp motor was more than likely around 88 or 89 SAE net hp, dropping to 83 SAE net hp in 1971 or 72 when they lowered the compression ratio. Assuming no other major changes, a 5 or 6 hp drop makes a lot more sense than the apparent 19 hp drop from 102 to 83... the latter being an instance of apples vs oranges, so to speak.