Natural Gas, whether Methane other, does not compress easily or safely. LNG or Liquified Natural Gas is a cryogenic liquid, chilled way down to pretty extreme temps to get it to liqufy and allow sufficient volume of fuel without involving high pressures which would require heavy tankage. LPG is a separate thing altogether, being Butane and Propane in various combinations.
To run something on Methane biogas you would need a blimp-ish sized low pressure gas bag for any real usable range.
You're better off putting the blimp in your barn attic to run the house gas stove than strapping it to the roof of your car to drive around.
I believe E100 and B99 can be bought straight out of the pumps these days, or you can make your own. No modification needed with modern cars rated to use the stuff.
WVO or SVO needs some modifications,
heaters and filter/pump systems, or a dual tank system, there's plenty of info around, just search the forums here or find a specialist forum.