I cut mine down, tank should be 15 feet 10 inches long. when I did mine (several years ago) I did it in 3 pieces to try to keep the fuel fittings in correct proportions not the best angle, but you can get an idea. Got the Bicentenial unit for Christmas, May try something slightly different for that. FWIW, the fuel tank for GP 30 is pretty close to the correct size, but would require adding fuel fittings.
Here's a better side shot
This is from an ex Uper loco that was (and may still be ) destined to become a super detailed Milw 156. easier to see where cuts made on the gray
front truck had to be replaced
Rick