Top idea, I am going to be doing a 351W twin turbo running on straight gas into an e series wagon myself.
I advantages of using a wagon is the fact you can use twin standard LPG tanks or? Maybe twin manifold LPG tanks without taking much room up inside the cargo area, unlike sedans where you loose a lot of space.
I used to own a straight gas XF Ghia wagon fitted with a healthy 351C and I would recommend fitting twin tanks because of limited range you may get out of running one, I ran out of gas once 40kms south of Rockhampton at 4am in the morning. (A lot of LPG servos are not 24hr).
And Rocky was where I was heading.
There are plenty of choices in gas system you can use, GRA (Gas Research Australia)
is one of the better known performance systems and there are plenty of others.
Another choice in the future is using gas vapour injection from ©Gas Injection Technologies Pty Ltd
and you could use factory injection harness and ecu.
What will be supplied is special designed gas vapour injectors that replace the petrol injectors; it will use a special fuel rail and regulator.
The rest of the gas system will be as per any other gas system, the idea mainly of the system is reduced labour costs eg tunning, better performance and none of the over faults with using a dual fuel system.
This system when released probably could be tuned for even better performance with a "Tweecer" etc as the ecu settings are for petrol and basically it will only be self tunning for emissions etc not best timing etc to suit LPG.
Best of all it will run like any other EFI car except it will be using LPG.
I have been communicating with Bill Campbell from http://www.gas-injection.com/index.htm
and he first replied with this email.
I will apologise for not answering but as we are in research there are times where the research takes priority. I am pushing as hard as I can to have some systems ready at the end of the year. It will fit a wide variety of vehicles and for performance oriented people like yourself we will be supplying basic components to your licensed gas installer and you can organise to make the adaptors etc to suit the engine. An example is we converted a Toyota 4AG engine with separate throttle bodies (see attached photos). The only problem is we are restricted in the flow rate at the moment so any wild turbo or supercharging will not be able to supply enough gas.
Gas Injection Technologies Pty Ltd.
Ph: 02 9632 4444
Fx: 02 9721 2201
As I want to use a twin turbo setup it looks like I may have a few problems with gas supply, but I am willing to give it a go and see if I can find another way around it, even if I have to use extra boost enrichment injectors and an extra regulator.