I've made the panels that close off the cockpit lockers easily removed for better access. This shot is taken from a few inches in front of the steering quadrant(I'm holding the camera from the port locker). You can see the exposed manifold connection and the two raw water hoses (one goes into the elbow - the other straight out the stern). The L bracket on the underside of the cockpit sole hung the old exhaust.
Here's a closer shot.
The horizontal line is about where the water line outside the boat is.
The blue rectangle is the muffler. I went for a larger capacity (gallon and half) and 2 3/8" hose. I hope to mount it on a plywood stand, to the port engine bed just aft of the engine and next to the transmission. The reason for that forward location is it leaves the whole area aft of the engine, for working, and it new muffler won't block access to anything(the white bilge pump line will be moved).
That area beneath the manhole is a comfortable place to work that would be spoiled if the muffler was placed there. I sit on the fiberglass bulkhead that supports the bronze shaft log with my feet on each side of the coupling. I've spent a lot of hours there, some quite pleasant,...
The blue lines: the proposed riser which will rise about 6" - then straight down to the muffler. Should get me at least 12" from the muffler top and not be too close to bottom of the cockpit sole. I haven't decided on a vented loop location but it could rise another 14" to under the bridgedeck(the bottom of the bridgedeck is in the galley).
Then the exit line will go straight up - to just beneath the sole - and follow the sole until it rises again to beneath the aft deck. Then it's down hill to the outlet which is 12+" above the waterline.