I love those old Big Boys- looks like you did a great job on this one.
Most people alive today have no idea how truly flippin massive these monsters were. The main driving wheels, of which there were sixteen per side, were 68" drivers- that's 5' 8" tall. There were a total of thirty-two of them on the locomotive. The locomotive itself was 85 feet long with a 72 foot wheelbase. Add the pilot gear and tender and the overall length is about 130 feet. At about 16 feet tall from the rail-head, it's longer and taller than most single story homes. Seeing one of these behemoths in person, resting cold and dormant, is an impressive sight to say the least. To see one of these titans alive, breathing fire and hot steam, would be truly awe-inspiring.
edit: I was curious, so I crunched the numbers and found that a 1:25 scale Big Boy would be about 5' 2" long and around 7" tall!