[Aerkuld]

Having gone down a similar path on my 996 you're faced with two options;
1) Find a replacement engine. This will likely cost ~$10k. The downside is you have an engine with no history, and no way of knowing if something will fail on that.
2) Rebuild the engine. IF it's rebuildable this is likely to cost at least $12k. The positive is you're able rebuild it with some of the reworked internals from someone like LN Engineering to improve reliability. You'll end up with a known quantity that's better than the original. That will allow for further track use, or just better piece of mind on the road.

First step would be to pull the engine, get a borescope in there, and find out what's wrong and whether it can be rebuilt. The engines coming out anyway regardless of what you plan to do, so get it out and check.