Hi turboco1 I know one case of converting Westinghouse 120 MW model W501D5A from liquid fuel to LNG. This plant is locate in Dominican Republic Santo Domingo, the name´s plant is Los Mina and the owner is AES Corp. Basically Los Mina people need to do many changes for use LNG main fuel, they need to change the fuel nozzles, add a LNG manifold, gas filter, install gas detectors into Turbine enclosure, modify and make some changes in logic control system (They need to create new schematics, ladder diagrams, etc). Of course they install all pipes, valves, instrumentation to carry the LNG from storage tank near to CT.
May be SW people can help you with this. Contact engineer Frank Gomez in SW (office phone number 407-7362298 and his e-mail is frank.gomez@siemens.com.
Unfortunely the person that make all changes is not work anymore in Los Mina plant.