Yes, with used engines you may be right. I don't think all engines suffer from this problem, but there is a risk.
Have you contacted Porsche?
I know for a fact that they sell the so called
Partiel motor Comprising: Crankcase, Connecting rods, Crankshaft, Pistons, Oil pump, Timing chain - this is from the US_GB KAT for my car 987 Boxster Base. Essentially this is just the core, nothing else - no flywheel, intake, exhaust etc. but this is all you need. Everything else needs to be transferred from your old engine to the new one. Porsche invoice price for this type engine in 2011 was $3200.27. For your car it's probably going to be more expensive but it is an option definitely worth exploring. I don't know if Porsche sells this to the public or dealers only but I am sure with some arm twisting you may find a way around the limitations. Good luck! I am attaching a picture just for reference of what you get.