Dear Mats, there are few wrong things with your zrf, I think.
1) in all Shatranj, promotion is only for a Firzan (Fers, Queen). Never
for something else. (Whatever is on the board)
2) victory is also obtained by bare king, not only by checkmate and
stalemate. This was - by far - the most frequent form of victory. There
is
an exception if the bare king can also take the last opposing piece in
the
next turn, in this case it is a draw.
3) problems also with the die versions: a king shouldn't be able to move
himself under a check, independently of what can be obtained with the
die.
Also, a player having his king under check is not allowed to move any
other piece except to remove the check. Otherwise he should wait for a 6
to move his king away from check. This is probably difficult to program,
but it is the true rules.
Cheers. JL