Brednul,
AA42 and AA40 pieces are identical - made in the same color and size. I am a piece fanatic and I have spare sets for every A&A made (over 10,000 pieces I think now).
It is a great idea to have an AA42 game for extras, Minor complexes, AA guns - check out my thread on the global board for new major complex plastic pieces for $2.50 shipped.