[updraught]

A quick look at that link, and as I alluded to above dual fuel with a carby does not give the best performance. Straight gas (propane) is better. Raising the compression is better. Yes, the distributor curve is different. There isn't as much energy in gas.
A low horsepower engine losing a few horsepower probably isn't a good thing. If you have plenty of horses to spare, you probably won't notice.

The newer computer controlled units are a different kettle of fish altogether.

If the engine has any weakness in the ignition or engine sensors it will likely show up on gas more so than petrol.