I had a similar issue for M.A.X. (Mechanized assault & exploration), and found a pretty weird workaround for typing keys using alt-gr under Dosbox, in-game.
Press & hold ctrl
Press & hold alt-GR
Press & RELEASE target key (e.g. "3" for # or "8" for "[", on french keyboard)
Release ctrl
Press as many target keys (ones using alt-GR) as you need (works normally)
And at last only, release alt-gr.
I'm not certain it works the same for M&M as for MAX, but my post isn't intended for the OP anyway, since his (old problem) seems solved already.
Finding infos about this kind of specific issues is quite a hassle, so I don't want it lost... and guess I might not be the only one ending-up here looking for that.