I've had a look through the transpose from (? K: is in the abc and possibly more than once) /to possibilities and it's going to be difficult and I'm not sure if/when we might have a go at it.

What I have done is added a javascript "calculator" at the bottom of the page which I hope will help a little.

The whole business of keys seems a little odd btw. abcm2ps seems to write D# as Eb and that's before trying to work out what abc2abc might do. Still I'd guess most works out OK for our folk purposes.