rocket mass heater with Stirling engine generator

I'm going to be making a rocket mass heater to heat a polycrub in the colder months.
it's for a community growing space and we are completely off the grid so I've been looking at power sources.
has anyone ever integrated a Stirling engine to a rms?
I'm thinking its killing 2 birds with one stone.

I don't know about "integrated", but some people have certainly mentioned putting a Stirling engine on top of a RMH barrel or the like.

I'll wait till I've got the rmh up and running and see then.
is there anything other than cob that can be used as a good mass?
I'm going to download the dvd set also

So far as I know, there are no commercially available sterling engines that produce useful amounts of output. This is especially true for anything designed to work with a solid fuel burning device like a rmh.

If you are aware of one, I would love to know about it.

The Stirling engines I have seen in this application have been running a little fan to spread hot air, or a small lightbulb or maybe electronic charger. Certainly not anything you would call "providing power" for a house.

One thing to really keep in mind if you decide to do this is paying attention to the hot versus cold side of the Stirling equation. From experience, I've had Stirling designed wood stove fans that work for a short period, but because the differential temperature cannot be maintained, stop working soon after they start running. The temp differential is KEY to Stirling performance: http://peswiki.com/images/0/0c/Stirling_engine_diagram.gif

If you want appreciable power I think a gasifier with thermal mass on the generator exhaust would be the best bet, but I don't think the heat would be significant.