The best way to convert an EFI engine is with a propane injection system. There are a few EPA-certified injection available for Ford vehicles but I am not aware of any for the 2.9L engine. OBDII-compliant universal propane injection systems are available from Impco/BRC, ECO, Prins, and Technocarb but cannot be commercially installed in the USA due to the lack of EPA certification. The work involved in converting any EFI engine similar to my 2003 Impala propane conversion.
It would probably be best to convert to a carb, those systems really aren't that complicated and you could install it yourself if you know your way around an engine. You probably dont have to worry about emissions because propane burns much cleaner than gas.