There is no separate 'east-west' board in the avant, apart from that: i've heard that the newer generation avants (=RF) has boards with 'addresses', unique for that avant and could only be dealer-changed (however, it does sound a bit like sci-fi to me).
On the other hand, knowing B&O, it wouldn't surprise me that, apart from the deflection board, most boards are alike and maybe interchangeable :).
Why the question ??, because if you have both you can compare the boards ?? :)
Sorry for not having an answer yet, will try to stick me nose into an RF when i get the chance (but you don't find these broken thus cheap around really.....apart from the tube in the curved avants i rarely see other problems with avants).