If doing this why bother with an antiquated ECU like a L8 ?
With the mods you want and the resultant cost it would be cheaper to have a aftermarket ecu with so many more features and much better adaptability for the future where cossie parts become obsolete.
Doing the mods you want it is in my opinion to even think about a L8, aftermarket ecu's run coilpack direct, do closed loop Al, LC in gear adjustable boost triple map etc etc etc.
Imagine it 3 years down the line your car needs a new sesnor of some sort, no longer made, can't find a decent one anywhere at any price let alone a reasonable uninflated price, what do you do, if L8 nothing end of the line!!
Aftermarket ecu, what do you do, get ANY sensor of that type of any car and it can be made to work, PERFECTLY, some even without a visit to the workshop.
Aftermarket ecu will do learn as you drive, offer fourth adaptive mapping from one load cell to another, boost control set against rpm/AND TPS, individual cylinder trims of fuel and ignition, movable speed sites down to 1RPM.
In short bin the ECU idea and go aftermarket as it's a better and B cheaper with all the bits, that a L8 can only dream of.
You would be better of asking how much power you want to end up with and work towards that goal.
tabetha