my dolphin came to me with the weber. i have used this carb many times on datsun 510's and 620 pick ups.
easy to install. the air filter adapter is a must if you need it to smog, but the standard oblong k&n type works better
look on ebay as they come up occasionally
your exhaust is factory. unless you do other mods to the engine(cam, intake, carb) i don't think it'll get you much. the o2s is a part of the system, as such removing it can cause some complications.
i have a weber 32/36 carb, and i think it's the most bang for the buck
when lighting my fridge, there is no flash when the fire is already lit. maybe wait a while.
the water heater takes a long time to get the gas through the pilot. fingers get tired of holding the pilot button
i bet the furnace is the same deal. turn it on and off a bunch of times
anything that needs 120v ac power needs the power from the pole or a generator. the converter (120v ac to 12v dc) uses some energy to do its job, hence the heat.
all the 12v stuff always runs off the "boat battery", the converter keeps it charged.'
as said, the fridge runs on propane---no electricity needed. the furnace uses 12v from your battery to run the fan