I am looking into converting my EF XR8 into straight gas using 2x425 Impco's and a m112 supercharger in a drawthrough system.

What changes will i have to make to the ignition and fuel systems (ECU)
to make this work.

Thanks.

If your getting the gas installed professionally they will get it running well for you.
If your going straight gas (and never plan to use petrol again) you could advance the ignition timing on the dizzy and tune your super charger down to 8psi (like the new holdens have for efficiency).

You could take 20thou off the head (really expensive though ~$1500) maybe just wait until you blow a gasket.

Keep your tyres pumped up around 42-44psi (everyone in the tyre world says thats too high, but at the advanced driving course i went to they said to do this) You get ALOT less / almost no tyre roll, you lose a little grip but you gain control, increase rolling resistance etc.
You'll understand what i mean once you have done it
Hope that helps
Matt