The posted tank dimensions sound correct for a P-38 tank, but these are typically referred to as a 315 gallon tank. The aluminum originals bolted together at the seam line.
Ben, you said you have a 300 gal tank like the Old Crow tank. These were a Navy Mark 8 standard tank, sometimes referred to as Hellcat tank, but mostly used on a Navy Albatross seaplane. These tanks are around 30" diameter at the widest point, not counting the flange, 13'6" long, and the two halves are welded together. This is what my tanks were, attached are some pics of the original decals. These tanks have a much different shape than the P-38, longer, skinnier, and a less pointy tail.
There are at least two other tank sizes with the same basic shape, one much smaller at 24" dia. and around 11' long, another at 32" dia. and about 14'6" long. I would suggest cutting open the tank you got and taking some actual measurements to verify what you have. Even my cad model of the tank is only approximate, any given cross section of the tank in my model is round, in reality it is an oval. Because of this my cad was only a starting point and final fitting of components often required a combination of test fits, mirrors, and checking clearance with a piece of 1/8" tig wire.
If you can verify your tank is the same as mine i will share the dimensions, but knowing there were numerous versions I would highly suggest double checking your actual tank before moving forward.
And yes, it can all be fit inside the standard length tank, it is challenging and can be a pain to work on.
Andy
