Marc, I will typically run 1960's-90's diesels together based on mergers. In my mind, they are prototypical but I admit that I never investigate much further. I don't look up the real-life engine rosters. I just want to know if it's plausible that the two engines could have been seen together at some point. So I run a SD40-2 Frisco with a SD40-2 Burlington Northern, or Missouri Pacific with Union Pacific, MKT with Union Pacific, etc.
There are a couple big freight yards here in St. Louis where I still see fading paint schemes like BN and Santa Fe. That inspired me to buy these two engines and run them together: