Darryl,
You are going to spend a lot of money changing things until your car is "fixed"
Has the pressure been checked @10psi when the car falls on it's face?
There are so many things to look at.....
Timing isn't going to affect how "lean" your car runs, although checking it will be a good thing.
Things I would consider when it comes to the fuel system:
Filter
Pump checking Volume and pressure
injectors
regulator
Which leads me back to the diagnosis, I'm pretty sure most cars will increase idle speed when you inject propane into the system, running good or not.
Maybe your car runs bad because the headgasket is gone, maybe your car runs out of steam because your turbo is shot.
There's too many things to consider, but you need to invest in a good quality manual and do some trouble shooting as it recommends.
I'd tell you to search online, but there's way too much voodoo fixes out there. "I fixed my power windows and now I get 500miles/tank."
Buy the injectors, so that they can be used as an upgrade. I'd guess 1 in 3 chance that they fix your problem. Not to mention a stock pump won't fully deliver enough to 550's anyway.
Good luck