I've been trying to find out something about the thin but wide aluminum device which is attached where the bowl would go. It seems that Honda does sell "dry fuel" parts and also sell vapor fueled engines.
That same carb on the Honda, if you added a 90 degree turn-down elbow which connects to intake, and a 90 degree elbow turn-up, which the breather sits on, would be nearly identical to my Briggs 2bbl. It looks like the Honda carb was designed to be used sitting with venturi bore running vertical, while my Briggs sits with the venturi bores running horizontal. Both choke and throttle butterflies look identical on each.
Honda just left off the bowl and float, removed the main jets and placed "spud-in" tubes where the jets were, then uses the aluminum thin/wide vessel to replace the gasoline style bowl and installed a propane supply. I can't find the Honda part (bowl replacement) like I see on this engine so far,, but Honda authorized repair companies can by logging on to order. Today was the first mention of "dry fuels" officially by Honda Inc. I have ever heard. But still,, the carb is a dedicated propane carb and not a tri-fuel.