Very interesting. Our fuel tank is an integral part of the keel structure. Holds about 40 gallons. It located below the engine. The access port (for cleanout) is just forward of the engine. Near the access port are the fuel filler line, the fuel supply line and the fuel return line from the diesel engine.
There is plenty of room under the cockpit floor for a fuel tank, mounted to the hull above and aft of the propeller shaft.
Was your tank added to "Magic" as a substitute for the one in the keel or did your keel not have a built-in tank? Is the filling fitting for your tank in the floor of the cockpit? Mine is on the side deck, port side.
There must have been serious differences in the way Lee Creekmore designed and built 36s. For example mine has a centerboard; yours does not. Otherwise the long keel and rudder attachment look to be the same.
Let's keep the conversation flowing.