I have built plenty of high performance engines in the 60's and early 70's...that's big blocks. If the engine is properly oiled and not run to low on oil, then these particles are not from the cam bearings or crank shaft bearings. These parts are usually made from a soft billet material and when run low on oil they can get scratched from friction and cause engine failure. Your particles could be left over residue from the original casting that has finally made their way to the filter. The only place that gets a lot of friction comes from the pistons as they slide back & forth during combustion. And this one reason for filters...to clean the oil. JB
Now, I have not been into a Porche engine since the 70's when they were air cooled, but basically an engine is an engine. They all work the same way. I would have a Porsche dealer take a look just to make sure there is no real problem.
