Hello all,
My above comment was in fact the Airbus reply to the same question raised by me (thru my company) some years ago.
Regarding the mixing of F/CTL computers:
There is nothing called ELAC 1 or ELAC 2 but ELAC computer until it is fitted in the a/c. The slot, in avionics compt, where the computer has been plugged in will determine it's number. (the same applies to SECs)