I have recently become interested in doing a Cepheus Engine (open source Traveler) conversion. I was working on a conversion of Cepheus Modern (
https://www.drivethrurpg.com/product...Cepheus-Modern) but there is now a guy on the Cepheus Engine Facebook group doing a conversion that is specifically geared to use with a Morrow Project of Twilight 2000 setting.
It looks interesting so far and he definitely "gets" Morrow Project and just wants a system that gives more than just a crunchy combat system.
Cepheus Engine has a small but strong community playing and developing for it. There is a crunchier conversions called Cepheus Modern War that is worth a look as well. It is really focused on small unit combat (
https://www.drivethrurpg.com/product/304503/Modern-War).
Definitely worth a look. Cepheus Modern is "Pay What You Want".