If you have a Firman dual fuel inverter generator of the WH series, you can easily convert it to run on natural gas using the pre-existing propane regulator equipment. Simply swap out the propane fitting for a natural gas hose quick disconnect. Everything should work as it would using propane but you may find the need to keep the choke pulled out a bit to keep the engine running smoothly. This shim can be printed and used to keep the choke pulled out about 10mm which is the amount that I have found works best on my machine where I live at around 4,800 ft altitude. You may need more or less choke so just adjust the thickness of the model in your slicer as necessary.
Youtube video showing the simple mod:
The author marked this model as their own original creation.