FOUND: Lionel 2023 SP Orange Passenger Set

My son and I have been playing with O/O27 scale trains for a few years and yesterday we came across this set of seemingly older (1960's?) engines and passengers cars. I cannot find references to the Southern Pacific engines and passenger cars in the orange scheme and am looking to understand what we found here. The engines have 2023 marked on the side which would indicate Alco FAs made in 1950 but really I do not know as all articles I can find say these were only produced with Union Pacific variations and speak about the directional switch which this one does not have. - please help! Passenger cars are marked 2483, 2484 (observation), 2485, 2486 (tail).

BTW - it is beautiful set with AB engines, two passenger cars, an observation car and a tail car with lights on back. this is our second Diesel and get a lot of fun out of them.