Instead of a quarter berth, it has a full aft cabin. The aft cabin is large, almost too large, but not tall. The port side of the aft cabin has a higher ceiling where you can comfortably sit upright, but the rest is pretty low in order to accommodate the cockpit above. It's definitely nice to have a full aft cabin, but it comes at the cost of shallow cockpit lazarettes.
The head? It's pretty decent I suppose. I wouldn't call it comfortable, but it's perfectly sufficient. You shouldn't have any problem standing there or the galley or the saloon. Headroom is pretty good.
If you make the trip, look/ask about any water ingress issues. Any boat will have leaks, but the aft wall of my anchor locker has a lot of water damage and needs to be rebuilt. When it rains it comes in through the anchor locker and eventually drains into the bilge. Also look for staining on the aft bulkhead in the aft cabin. The hull to deck seam under the rub-rail at the transom is worthy of suspicion for leakage. Search the forum for "rub rail adventure" if you're interested in getting a look at a leaky 306 rub-rail.
Good luck and enjoy the trip!