as per the title, what do I need to do to go straight gas in my EF V8, there's the plumbing I know, but what's needed in regards to ECU and electronics etc.

Is it already on duel fuel or are you converting from stragiht petrol to straight LPG.
Basically all you need is a normal type LPG kit, but with the stragiht LPG they put some plunger/primer thingo in so that it can start on LPG (duel fuel setups generally lack this - and although most will tell you there duel fuel does start on LPG, truth is usually they don't, the electronic controller automatically recognises that the switch is still in LPG mode, and so automatically switchs back to petrol to start and then once started switchs to LPG).
If you do go straight LPG, it's personal chocie weather you remove the petrol system or not...

I'm will be going from straight petrol, and removing the fuel tank, I want to put twin exhausts on, 1 each side and I'm told I need to remove the tank to achieve this.

do I need to change cams, and remap the ECU etc