I have a 2013 G37 journey that overheated the other day. After some troubleshooting I discovered coolant was filled in one of the spark plug wells indicating blown head gasket.

Now I’m torn between tearing down the engine to replace the head gasket or just replacing the engine.

Looking for some help deciding what will give me the best reliability moving forward.

Whether it's worth the effort (which is very considerable on a vVEL VQ) depends a lot on the severity of the overheat. If it was just a minor overheat causing an old gasket to fail and the engine was stopped immediately, there's a good chance the heads are okay and replacing gaskets may be worthwhile. If it was a bad overheat or driven hot for very long, it's likely the decks are warped, which is a huge can of vVEL worms.