I have access to a dual fuel EF and, to this point, we have only had a few problems. It is a Tickford system, where the computer has been spoken to regarding to changes from LPG to petrol
Over approx 90,000 km:
1) Original owner must have had some work done one the car as the converter had an air lock and would freeze. Once found and fixed, no problem
2) Running car on gas is less economical than petrol as far as Kms/l go. The initial cost of a tankfull of petrol is a killer though.
3) Running the car on gas disguised the fact that the o-rings on the injectors were stuffed.
4) bad leads caused the car to backfire on LPG. Once found and fixed , no problem. Replaced coil pack at the same time.
5) need to use good quality oil, needless to say, and strict oil change intervals as the LPG has acids that can build up in the oils and affect the bearings.
Overall, no real problems whatsoever (touch wood) despite what a lot of people have said about the Tickford system, including Gasresearch who tried to sell me one of their systems when the converter was freezing.
As far as mods go., I have a 351C that is dedicated gas. It has had headwork done by my favourite head jobber. All he needed to know was that it was LPG. It has a cam designed for LPG (Crow). dizzy mods to suit gas. extractors. Goes quite well
Forced induction systems for LPG are not uncommon, and have been around for quite a few years, and I am sure that there are drag cars running in the States with LPG forced induction, although I don't know of any in Oz.
Yes, gas does give you less power, but it depends what you are after. Petrol in traffic light drags, and gas when you blow the other car into the weeds. The change in this EF is instantaneous, only a slight hiccup from the engine
Keep the rubber side down