yes the lister can run on natural gas, but only in dual fuel mode.
there will still have to be some diesel injected to initiate the combustion cycle, as natural gas has too high of an octane rating to fire in a diesel engine. it is good that this is so because unless you direct injected it at the proper time it would detonate.
there are two theories of operation here
theory one: if natural gas is admitted into the intake stream, and is ignited on the combustion stroke the tendancy would be for the engine to gain rpm, the govenor would taper back the amount of diesel injected to stabilize rpm, up until sufficient natural gas is entering the engine and the govenor cuts back sufficiently to fall under the pilot needs to initiate combustion.
theory two: this is where a natural gas/propane carb is installed to deliver the gaseous fuel, and another govenor is used to tailor the fuel delivered.
do a web search on dual fuel operation.
also it should be noted that there are associated problems with flame front travel on larger engines, smaller bore engines are more tolerant.
i would like to know of those that use propane injectors on their listeroids, when injecting propane, does the engine rpm rise? does the fuel rack retreat when propane is injected?
bob g