I've recently needed to prove my 968 is unmodified to the French federation for old cars, part of that proof included a photo showing my engine number and a recent newspaper displaying the date; not an easy task given the location of the engine number. Here it all is .....
It's on a horizontal tab near pot 4 exhaust. You can now see most of the stamp, but the final character is obscured by the nut holding the exhaust manifold in place.
Initially I had an idea where to look but could see no evidence of any characters at all; understandably years of road grime had settled on the plate. I squirted WD40 onto the plate in the hope I was in the right place, let it work for a little while and then scraped with a long flat-head screwdriver. The code began to be revealed. Then using one of those long flexible rod thingies for picking up dropped washers etc (no idea of the name) I grabbed a wad of cloth about 1" square and soaked it in white spirit. Rubbed it across the plate and hey presto!
Using the pot cam revealed the final digit and allowed me to include the newspaper in the photo at the same time.
I hope the photos help.
My thanks to Waylander, helpful as ever.