[Retroman1969]

There's probably no need to clarify that from an investment standpoint, dumping money on a big repair on any used car is a bad idea.
However, if the engine goes in mine I will replace it. I enjoy the car, and I know the car well. I know all the maintenance is up-to-date. If I dumped it and went out and bought another used car to replace it (I hold this feeling for any used car, not just Porsches) then I would be starting over again, taking a gamble on a car with which I'm unfamiliar.
The only time I'd think differently is if I don't like the car, am tired of it, or it has like 200,000+ miles on it and is a tired piece of junk.
If you like the car, I'd find a reputable Indy Porsche shop. They can source good low mileage used engines, check the chains and tensioners, and replace (and upgrade) the water pump and IMS bearing upon installation.

This is just personal opinion based on my experience with driving used cars over the years.