i have the same problem with my own 62 tempest that im' estorin. i found out pontiac acadian is slightly smaller and deeper but fits, theonly difference is the filler that you should use the oriignal. so some modification would work. let me know if the buidk works ornor(regarding the previous answer) good luck

Sources: 1963 pontiac acadian, 2 door

1961-1962 4 door Buick Special gas tank will supposedly interchange. station wagons will not...