Factory EFI A body conversion

If performance engine changes are a priority now or in the future, the factory ECU might not be the best way forward. And a 408 is pretty far from stock already. A universal aftermarket engine management computer like a Megasquirt will work better in the long run. You could use OEM components for just about everything, although a better intake manifold (Hughes does an EFI air gap) and higher flow injectors will be needed regardless of the ECU choice. Is your engine Magnum or LA?