Spare tire help

Working on '68 cuda FB with E70x14 redlines. This oversize tire option causes the spare tire to stick up further from the spare tire well. This requires a longer hold down bolt to secure the spare. Mine is missing. The standard length is about 7 1/4". The parts book lists the proper one as 8 3/16". Does anyone have one I can purchase? See picture of "incorrect" one.Thanks for the help.100_2180.JPG