Yes. I converted a 8000w Briggs and Stratton Elite series portable generator when i first got it. Never put a drop of gasoline in it. It will run on either gasoline or propane. I have a bunch of 20lb tanks and one 100lb tank. The 100lb stays stored for the real emergency. The 20lbs are for my grill and the generator. I can get about 6-8 hours on straight full run on one 20lb tank. I love it. Never worry about storing gasoline that can go bad or gum up the carb and lines. I do have to make sure I keep up with oil changes and I use synthetic as the combustion is hotter than gasoline, but the generator hasn't overheated. The only issue with LP gas is if it is really cold. The small 20lb tanks can freeze before being fully emptied. The fuel consumption rate cools the tank and in the cold can do so too quick. One option is to use a larger tank like a 40lb or I just swap the 20lb tanks after a few hours, let it warm up and swap it again. No big deal.
Google propane generator conversion. There are many options. This is one
http://www.propane-generators.com/
It's been a few years and I think I used this one, but can't remember exactly.
http://www.propanecarbs.com/tri_fuel_kits.html It worked great. Had to cut the frame of the generator just a bit to fit the extension ring on the carb, but different generators will be different. I highly recommend it to anyone with a portable genny.