[sailingdog]

IIRC, you have to change out the hoses and regulator as well... since the hoses are very different. From another website:

LPG (propane) or CNG (compressed natural gas) hoses, which either constitute the supply line or make the flexible connection from a copper supply line to a gimbaled galley stove, are clearly a critical safety item. For LPG systems, ABYC Al, Marine Liquefied Petroleum Gas/LPG/ Systems, requires that the hose should be marked as complying with "UL 21 LP Gas Hose"; while A22, Marine Compressed Natural Gas /CNG/ Systems, states that CNG hose should be marked as complying with "NFPA (National Fire Protection Association) 52." In both cases, the standards call for end fittings to be permanently attached. Swaging is one acceptable method of attachment; a hose clamp is not.

The two standards also specify that every appliance should be served by a continuous fuel line (that is, one with no joints or connections) from the gas cylinder regulator to the appliance or, in the case of gimbaled stoves, to a length of flexible hose connecting to the appliance. This means that if a boat has more than one gas appliance, it is unacceptable to run a common supply line, and then tee off this line to the devices. Any connections or tees must be made inside the gas-bottle locker which, if designed according to the standards, will be sealed to the accommodation spaces and vented overboard. This will keep any gas leaks from the connections or tees out of the boat.