[Porsche-O-Phile]

Realistic worst case scenarios are a snapped timing belt (new valves, possibly new pistons, possibly a new head), an overheat (warped head), a spun #2 rod bearing or either a blown out head gasket or oil cooler seals.

Any of them are fixable by a dedicated DIY-er. Or you can buy a used n/a engine for around $1k and transplant it in for about the same amount of effort, get the car running and then figure out what's going on with the original engine while it's out of the car and on a stand where it's easy to work on. That'd be my recommendation.