Shawn, there was a suggestion this thread was merged with:
http://www.pprune.org/forums/showthread.php?t=226000
This engine is a clever concept, but i'm not convinced. It needs complex seals, bearing in mind the 25:1 compression ratio. These will require rotary level of development, but for pressures of two to three times greater. Oil emission will be much worse than rotary.
The mechanism also looks much too flimsy for the sorts of powers discussed. By the time it is beefed up, i'm betting the weight is nearer those V8s that are mentioned. I would imagine compacting the mechanism is on the menu.
Mart
Edit: To address Delta3's comments about rotary seals.