My '98 +4 is allegedly 11 gallons (55 litres). Never got to the stage of putting more than 46 in on a fill up. By then the gauge was nudging 'not a lot' and without a spare can of fuel my nerves were giving up!

Usually run over 300 miles before filling - long trips over 330. The '76 definitely has a smaller tank, but I regularly run in excess of 200 miles before filling...
Cheers,