EE here as well.
A natgas engine will run on propane, but you need a regulator.
The natgas grid will survive for a long time after the elect grid is down, 6 months at least, if there isn’t something actively interfering.
Listen to the Steven Harris interviews on thesurvivalpodcast.com for more really interesting alt-E stuff.
Do you think Nat Gas will function and distribute countrywide after any EMP ? Are there not valves/switches in the pipelines that are controlled with computer gear. I don’t have faith that anybody has tested the ‘gas-grid’ for EMP integrity