Well I have been offline for a few days and it looks you boys and girls have been having fun off topic.
I was offered two complete Thor manifolds with wiring looms for a really good price so that is the direction I will be going.
Just need to sort the ECU aspect - most likely MS but happy to hear from anyone who is running a Thor on their 4.6 with a different ECU.
As I paid some decent money for the cam that will go in my new engine I don't want to stuff up its running in so I will move the carbies across from my 3.5 to just run in the engine and cam as they work perfectly. The cam needs to be run for half an hour at greater than 2500rpm and must not spend time cranking. I don't want to be stuffing around sorting injection systems with the new cam.
Once the engine and cam is run in, I will but the injection system on and go through the issue of sorting it to run properly on petrol. When it is running on petrol I will then install the LPG system so that it will run on dual fuel.
One step at a time.