Wow, what a story! At least I'm glad to find out that there are still people out there that stand behind their work, and are willing to go such great lengths to make things right. When I will need engine work for my car i know where to ship my car!! I am electrician and i always fix smaller things on my cost that were not included in the estimate, i just cant leave things alone that i know are wrong. So i see where are you coming from, except your costs in this case were quite large.
I do pretty much all the work on my car, but i would never touch the engine. Once i worked on a much simpler Mercedes engine and it was not pretty, tried to save some money, ended up towing the car to someone who knew what they are doing and ended up spending 3 times more than i would have if i never touched it my self. It was quite embarrassing
And one thing thats certainly true, the seller of the engine is definitely not a porsche enthusiasts. Hopefully eventually it will come up who he/she is.