Old as Dirt!
In the port aft cabin, there is a smaller hatch door in the bulkhead between the cabin and the engine compartment situated beneath the base of the berth, which is removable. It is awkward but doable. One must be careful not to damage the wiring from the fuel level gage sender near the top edge of the fuel tank above the muffler.Thanks for the info Letrappes. But I can imagine how did you get access to both ends of the muffler. For me seems impossible!
FWIW I suspect that everyone that owns a mid-80's era First 42 has gone through the exhaust hose replacement exercise or, if not, will. Ours cracked right above the exhaust through-hull in the bustle while we were enroute to Key West from Tampa Bay a few years ago. Fortunately, I had a roll of "Rescue Tape" aboard and was able to make temporary repairs but we had to deal with quite a flood for awhile. A real (literal) pain in the neck! When replacing the exhaust hose, you need the most flexible hose you can obtain, regardless of cost. Trust me! BTDT!