I believe your tank is beign reproduced. Check with Poston or Year one. Of course all '64-'65 "A" bodies have the same tank, BUT, the fillers are different so they won't fit! BUT, You can unsolder your filler and put it on a Chevelle tank. My brother did this on his '65 Convetible. This was about 10 years ago and the tank was still available from GM.
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Life long Buick fan,
1965 Gran Sport Conv.
1965 Skylark H/T
1948 Chevy P.U. with 401 in it.