As far as I know, the last released version was 1.5, and the last unreleased (but available) version was 1.6.

http://www.planetarypinball.com/mm5/Williams/tech/pin2000/software.html

http://mirror2.ipdb.org/files/4446/Bally_1999_Revenge_From_Mars_ROM_Revision_History.txt

Where did you find the 1.8?

By the way, 1.5, 1.6 were not the full versions of the code. they were patches only, that you would apply to your original system.

Nucore developed a special reader to pull-down the full version of the code from the masked ROMS

Those full versions were then patched/updated

The full versions were provided to Wayne for distribution, and you need the full code version for your Nucore system to run.

Chuck is here, and can chime in, if my statements are wrong.

Lastly, Big Guys company did have dedicated forum for Nucore support. I'm not sure if it is still active.

Dead as a doornail. The forum is still there, but I tried to register a while ago and my account never got activated so I could post.

You can contact Chuck here: http://pinside.com/pinball/community/pinsiders/chessiv

I have 1.0 running. Afraid to update it. If it ain't broke don't fix it?