There's just a whole different level of machining talent in building that compared to the V12 you posted.. Not knocking on either, both excellent pieces of work, but the amount of machining hours alone that would have gone into that are massive
Hands down that is very nice work, that being said if you look closely enough at the valve train you can see the valves float at RPM change. For a solid valve train to float like that this engine would not last long set up to run as a internal combustion engine.
There are miniature 'gas' engines both 8 and 12 cylinder on Youtube that are put together way more precisely then the pneumatic driven engine posted above.
Oh look, there's one here:
There Youtube channel: http://www.youtube.com/profile?annotation_id=annotation_508810&feature=iv&user=ArtusMotor&src_vid=mutb7KgA9NM
Look at the channel, a larger version of the 12 cylinder is videoed turning airplane props. IMO, the larger scale engine needs a improved exhaust system, but between 3,000 and 6,000 RPMs it's not to hesitant.