You should be able to use high or low pressure with the proper regulator.
I'm no expert on NG/LPG conversions, though.
I would like to state that you generally lose a %age of peak power when going from gasoline to NG or LPG.
I've seen NG/LPG conversion salesmen guys gloss over the loss of power and claim that converted gens run 10db quieter. The conversions generally run quieter, but I think 10db is exaggerated and I can not seem to find documented figures that show a 10db decrease in sound level.
IMO LGP/NG conversions offer convenience, long term storage benfits (LPG), are quieter, and are cleaner burning.
But, I think the people who sell conversions need to be up front about true efficiency, true gains in quietness, and true losses in gen power.
Please do you homework and if you do choose to convert, let us all know how quiet, powerful, and efficient the converted gen set is compared to the original gasoline setup.