Welcome to the best Vette forum reeltales, I can't say for certain on the mid-year cars if you can drop the tank, I assume you can. Mine is a '78 and like all of the C3's, the tank comes out from the bottom. Please be patient, someone here will give you the answer.
I have removed the crossmember that is below the tank and taken the nuts off of the tank straps. The tank will move around but appears to be too tight to just drop out the bottom. I do not want to try to force it out until I know for sure it will come out. There may be a trick to getting it out.
you remove straps holding tank and then you have to tilt up the end (toward front of car I think) and wiggle it out, it seems impossible but it WILL come out, done it several times on my 67 and in fact plan to do it soon. good luck.