Re: gas gauge
You might want to consider a Lowrance LMF-200 with an fuel flow sender and an EP90 water pressure sender. It'll take the place of the speedometer and fuel gauge while also offering you GPH and MPG. It will be vastly more accurate than a regular fuel gauge too. They are very easy to install and reasonably priced. You can also add other senders to it to read things like water temp, air temp, oil pressure, engine temp, etc. Once the wiring is installed, adding senders is extremely simple.