WOW, and i thought waukesha engine here in my hometown bult some big ones. Waukesha builds the diesels that run the pumps on the alaskan pipeline. The pistons in those are bigger than a 5 gallon bucket.
Cathedral engines are a gas, I love 'em. and they're more fuel efficient than any other engines on the planet (assuming you're measuring in kg/kw/h ofcourse)