So the computer will still be hooked up to the 12 volt system the engine will code out but will not effect the trans or transfer case my 5.3 distributor is going in the 327 and as far as the truck goes it was put into the truck before I bought it the efi is part of the ecm so it will just code out I just need to know what to do about the return lines on the tank and if the thumper on the 327 will pull fuel thru the in tank pump if its shut off