I believe there have been three versions of the Twilight 2000 rules. There was the first edition. Then Twilight 2000 version 2. And then they updated this book to Version 2.2 to make it compatible with Traveller: The New Era. Which of these Twilight 2000 rules did Cadillacs and Dinosaurs RPG use?
T2K Edition 1 is a wholly unrelated game engine.
House System version 1: Note that the GDW House System begins not in T2K, but in Space 1889. It later gets revised into T2K; it used 1d6 vs Skill + modfiers, or (Skill)d6's totaled vs a TN ala Star Wars, or (skill)d6's individually vs a TN by difficulty counting successes.
House System version 2: T2K Edition 2, aka T2K 2.0 is the 1d10 version, and also was used in Dark Conspiracy 1E. 3 Difficulty levels: 1d10 vs Skill x2, x1, and x1/2, Roll Low
House System Version 3: T2K Edition 2.2 is the 1d20 version, used in DC edition 2. 5 Difficulty levels, 1d20 vs (Stat+Skill) x4, x2, x1, x1/2, x1/4, Roll Low. Character Gen is identical to 2.0 save for a couple of errata entries. Combat is revised slightly.
House System Version 4: The 4th version of the House Engine is Traveller: The New Era. It makes many additional changes to 2.2's engine, especially in Character Generation and Combat. Equipment is compatible, and characters close.
Sometimes reference is made to T2K 2.1; no such rulebook was printed, but the upgrades to tasks of 2.2 were previewed in the Ref's Screen for 2.0, and some refer to that rules upgrade as 2.1; 2.2 made additional changes above and beyond those.
All of the Dark Conspiracy and T2K 2E materials are compatible, even with the change of dice mechanics in T2K2.2 and DC2.
Based upon the time released, and reviews online, I believe it's based upon T2K 2.0.
It can easily be "upgraded" to 2.2; the differences are few.
I will note that I never bought it because the Character Generation method was different from the T2K2/DC Character Generation. But note also: I've read (repeatedly over the many years) that C&D has other mechanical differences besides CGen.