Hello,
Zach pointed me to your remake last week. It seems very promising.
I've worked several years ago on the reverse engineering of the Atari 8bit version.
I haven't fully translated the document i wrote and I don't know if you aim using the original game behavior, but if you have any questions I'll be glad trying to help you (here or at
my forum).
I wish you all the best with Planet M.U.L.E.,
Kroah