fuel tank bolt question

I don't know if I should be in the parts section or not, but I need to know what size the bolts are for mounting the gas tank. Thread size, length, and the size of the square head. I am guessing they are 5/16-18, but since I don't know, any info someone might have would be very helpful. Thanks in advance!!!!

After a little more thought and searching, I am going to figure they are 1/2-13......and probably standard on all Ford vehicles around that era. Does anyone have a clue as to where I can get new ones. If not, I will just make a couple if someone can tell me what the head size is and what length. I will do a little more research on the car in the morning to see what I can find out about that also...shouldn't be too hard, I can always guess the length....