I don't know too much about how compressors are built, but the type in the story I heard was an old Mopar A/C compressor like this one:
It looks pretty durable to me (probably all cast iron) but again I don't know how the valves, lubrication system, or piston rings work. In the story I heard some guy living in the Alaskan wilderness used one of these hooked up to a homemade boiler/stove and an alternator to charge batteries and power his house, in conjunction with solar panels. Apparently they put out something like 3 hp with the right boiler. I haven't found much more info beyond that though.
I've thought about buying a compressor (they're pretty cheap on ebay) and building a boiler like yours, then mounting everything in an old motorcycle frame. But I don't know too much about what it would take to adapt the compressor into an engine, and I don't have the space, time, or money for a new project.