1966 gmc rear gas tank question

[1lo94]

So I am building a 66 GMC short stepside, I wanna move the tank from the inside to the rear frame section. I was curious about the LMC or Brothers 17 gallon top fill tanks. I did a big notch on the frame in anticipation of bagging the truck in the future and was looking for actual measurements of the tank itself, because I called both places and neither could give me the measurement of the tank without the flange included. I thought about a boyd tank but was trying to make the truck a little more budget friendly as I have another project I am working on as well but wanted to get this one on the road soon. Here are some pics as well