I've never seen one used for locomotive purposes, but my retired uncle has been tinkering with them. He built a couple, and I think one actually works!! However, lately, he has been building steam engines (not locomotives) that run on compressed air. Pretty cool stuff.
and this one is Gauge 0 and subject of an article in the magazine illustrated (copyright Magicalia, reproduced without permission under the Fair Use/ Fair Dealing terms of the copyright laws as a Review)
Used to go to the steam thresheree in Freeport IL. The main attraction was dozens of steam tractors, a shay loco and some big engines, but there was always a guy with a booth full of sterling engines he had made of cans and such clanking along. Always thought I'd try and make one of those.
Sorry for this late reply, but I couldn't find the magazine. Check out the November/December 2006 (Number 90) of Steam In The Garden. On page 19 Andy Ross describes his building of a Class A Climax using a Sterling Engine as the power plant. Very interesting and it WORKS!