What does the engine need and what are you expecting to pay? There are $30k rebuilds/improvements rom nationally recognized folk and $4k depending on what the engine needs.
Used to live near the circle, I'd seek out the local Porsche club (PCA) and go to one of their meetings and ask the locals. My mechanic got an inheritance and got out of the business ... he was the perfect one as he had many race preps=] cars around the shop and engines torn down and that is what you are looking for. Discovered him by driving by and observing what was in the parking lot and wandering around the shop but that was in the days before insurance companies started being strict.
Another source is the Potomac region newsletter at
https://pcapotomac.org/. Some of the ads I see are from places that were in business 20 years ago. You don't do that without some expertise.