The wood mountings make absolutely no sense to me; they cannot be elevated or depressed. Might they be for display or perhaps they were fitted to some sort of carriage and those were removed to facilitate easier shipping back to the States.
The one on the left looks like it was modified to take a rimmed cartridge; 37mm cartridge is what was used as an anti-tank round; I can't imagine putting a round that size in a gun approximately 14.5 inches long. Then again...
Edited to add link:
http://www.landships.info/landships/...chutz_M15.html
The Lantaka I can't tell about the breech as the photo you posted does not really show the rear, or breech end of the barrel clearly.
