Relocation Fuel Tank

[The Ledgend]

I purchased a fuel tank relocation from Automotive Parts Network. I got the tank to fit it is all looking good until I messured the fill hole and it mesures
1 1/4" O.D. then I went to the local parts store and they are unable to order that size. Then the filler neck that I ordered is 1 3/4" O.D. It is my own stupidity that I did not ask what size is the filler hole before I ordered it, but I thought it was all the same size, so now I am not sure what to do. Has anyone have any ideas or had this same problem. Any help would be greatly appreciated.