Propane has less energy per charge than gasoline.
EA81 or EA82 engine?
Anything you do will reduce the reliability. Cost a lot. Take a lot of time. To get small gains. Parts are rare, and getting scarcer.
Install a 2.2EJ engine. A lot of work, but real gains in power and reliability in the engine. And parts are still available. 40% HP increase may not be good for the rest of the drive line, but many have done it.