Installed a mechanical guage last year.
Have an 84 H34. Look in M & E Marine Catalog, (pg 198) price 37.95 for any size Tempo mechanical guage. Phone 800-541-6501. Measure the depth of your tank and go with a size guage that is the same depth or if not exact, a guage for a tank that is shallower than your tank. That way when the guage reads empty, the float will be hanging straight down, but you will still have some fuel left. Th amount of fuel left will be the difference between the guage you ordered and the real depth of your tank. I tapped the hole for the guage at the bow/leading edge of the tank and about in the middle between the port/starboard edge of the tank. This location made for easy reading and the hole serves as a pickup/clean out hole to suck out any gunk before installing the float device. Also you can easily reach the sump area where the pickup tube for your fuel system is as well as all the corners.To suck out the sludge, attach one of those rotary pumps to your drill with the discharge going into a bucket and a long pickup tube attached to a yard stick with plastic ties. This allows you to poke the tube in all corners and the sump area. Use clear plastic tubing to get a visual on where/how much sludge is coming out. The pick up tube needs to be a few feet long for the tank depth plus some footage to come outside into the cockpit where the drill is located. It helps to have someone operate the drill while you shift position of the pickup tube. The guage comes with all gaskets screws etc. and is not a problem to install. And I have not had any leakage. A real comfort to lift the lazerette and look at a guage. The hardest part after you empty the fenders, dock lines etc. is squeezing down into the hold to do the work. And it helps if you forgot something to have your helper go get the additional tool. My M&E catalog is a 1999, if they no longer carry it, Boat us has some Tempo guages but I don't see the selection, so give their special order dept a call or stop in to view their catalogs for sizes/part #s, or e-mail me with your specs and I'll look it ou in the 99 catalog for you.BOLPJ