While practicing touch & go takeoffs and landings on runway 25R at Long Beach International Airport, Long Beach, CA, the aircraft experienced a total engine power loss. The PIC was flying from the rear seat and reported the aircraft altitude was insufficient to return to LGB and land on runway 12, and he elected to land in an open area about 1/4 mile northwest of the airport. The front seat pilot/passenger took over the controls because he could see the emergency landing area better than the PIC. During the landing roll, the aircraft nosed over onto its back after colliding with some railroad tracks which were perpendicular to the aircraft ground roll. Both certificated airline transport pilots sustained minor injuries. Post-impact exam of the wreckage disclosed that the aircraft was out of fuel. The exam further disclosed that when two gallons of fuel were added in the fuel tank, the fuel sight gauge was not discernable from the front seat cockpit. The sight gauge is opaque. Flight time was not reported/unavailable.