I believe that Chris Westfalia (the mod) has made a number of templates for 1/56 vehicles, which are (were? ) posted on his Displaced Miniatures account.
Most free models are 1/72 scale, although there are the Polish kits, which are usually around 1/35 or 1/25. Either way, it's quite possible that you'll have to rescale.
http://www.toposolitario.com/workshop/steammecha.html This guy has a free walker kit.
And it reminds me, I should work on an upscaled version of my cardboard Gear Krieg models...