But very basically.(design doc aside)
Since you're held on to copyright it will be easier.
Here are few parts you can actually do with the original?
1. Move original to opensource GPLv3, porting it to sdl - lots of good people did that to their producs so they wouldn't go to waste - abuse, tyrian, warzone2100, ID does it periodically. I can take it upon myself and probably employ some programmers to finish up the code, include best parts from both versions (music from amiga, button and action sounds from dos, better graphics from amiga as well).
2. Do a release on gog.com of the original game (free even, as like tyrian did)
3. My version of the game i am planning to release is somewhat of a re-imagining with elements and usability added (in short - changes i decided upon in scale and usability are similar to changes between theme park and roller coaster tycoon) - focus shifter from arcade'ish top-down "first reach first serve" frustrated approach (really - that's the worst part of the original - frustration factor - cannot concentrate on managing efficently enough because of it) to more cautious "lot cost" system (once again - in design doc.). Additionally resource trading system should (and will be) changed like this:
*excerpt from design doc*
[*]Fourth stage is a trading stage. That’s where players sell/buy resources.
Note that buying off mike’s warehouse is always costly, and selling to mike’s warehouse is always dirt cheap.
So instead stage split on 2.
- Players throw out sell orders with checkbox(sell to other players, if nobody bought - sell to warehouse at the end of buy state). (price is at least 5$ higher than sell to warehouse).
Then players review sell orders of each other and decide to either buy from warehouse or buy from offer, if there’s any purchasing needs to be done.