Hey Chris, just a thought on getting that gas tank installed. I think your 64 is not much different than my 73 on gas tank.
If you're running dual exhaust and my car exhaust is 3 inch necked down to 2.5 after the mufflers and over the rear axle it goes.
If the gas tank is not lined up proper from side to side you could be a half inch off and it will rub on the exhaust pipe just a bit.
My opinion is not to tighten the tank bolts till you get the exhaust pipes in. Don't ask me how I know that.