There was another company building utility-scale stirling engines for a while for generation based on methane capture. If I can find it, I'll come back and post a link.

Here's one, but I don't think it's the same company I was thinking of because it's too small.

The trick was to seal everything inside a chamber to prevent leaks (generator, engine, etc).

Complex wobble-plate piston mechanisms.

There's always another chance to get DARPA money....

OTOH, if an actual engine manufacturer is working on it, there might be hope:

https://www.yanmar.com/global/about/technology/technical_review/2022/08_5.html