andreas: Are you sure of that? Caspablanca had a number of different games called Capablanca Chess. 10 × 10 board too. The Chess variants site has a few of his game designs there.

http://www.chessvariants.org/large.dir/capablanca.html

It shows four different games and mentions that the names of the pieces were called other things besides Chancellor and Archbishop, though it doesn't say what.

http://www.chessvariants.org/large.dir/bird.html
Predates Capablanca's Chess various versions by 40 or 50 years.

Embassy Chess is made up from Bird's Chess not Capablanca Chess. The names of the pieces are those used in Grand Chess. Bird named the pieces Guard and Equerry, but those names don't seem too popular. I personally don't like the names Chancellor and Archbishop. One is a school official and the other's name is part of a piece already on the board. Whereas Marshall and Cardinal seem like good names. Marshall is the second strongest piece on the board and is a military general. The Cardinal is a powerful Bishop that can change colors to have the power of two Bishops.

As for changing them, the letters should match the names of the piece where it is practical. I remember when I first learned to play Chess, the Knight was written as Kt. But it's been N for a long time. M for Marshall and C for Cardinal, seems simple to me. What's so special about A and C? The C is conflicting with the name of the pieces. The A doesn't match any of the pieces. At least with the N for Knight you have the sound of the word Knight and you eliminate confusion with the K for King.