LM, the company I work for a company that converts gas engines to propane all the time. First, propane is a pressurized fuel that ignites in the gaseous form. Gasoline ignites in the liquid form so the carburetors are completely different. I couldn't tell by the picture if your generator can use the three different fuel sources, gas, natural gas and propane. Make sure it is made for the other fuels. They will sell a conversion kit for the models made for propane.
Propane burns hotter and dryer. Because of the heat, make sure your motor has hardened valve seats or you will have a expensive wheel chock in less than 10 hours of running. We destroyed 2 engines from GM when they came out with a new model because they "saved money" by eliminating the hardened valve seats. In other words, if it wasn't made to run on propane, I wouldn't recommend converting it. You might end up scrapping a very nice generator.
Just some thoughts.