Where to start - maintenance on a 340

If you have coolant in the oil, and you did a cooling system pressure test, and it shows leakage.

Then I would suspect 3 places, and one concern.

1. The timing cover has rotted internally and is leaking into the block
2. The intake manifold gasket
3. The head gasket.
4. If the engine was stored with water in it and it froze, a crack could have developed