The train in the opening credits and closing scene is the Durango & Silverton Narrow Gauge Railroad sight-seeing train in Colorado.
As this was a Cherokee Production, which was James Garner's own production company, there are many familiar faces, faces of cast members who worked with Garner on his series, including The Rockford Files (1974).
At the end of the movie Jug (Jack Elam) presents an epilogue about the fate of the main characters from the caboose of the moving train. As for himself, he mentions that he goes on to star in spaghetti westerns. Actually, he is ironically referring to Elam's iconic, but all too brief, role at the beginning of Once Upon a Time in the West (1968), as the leader of a small group tasked with killing Charles Bronson's character (unsuccessfully, of course). Viewers don't even hear his real voice as he was dubbed for the English version of the movie. The only other spaghetti western he appeared in (credited) was Sartana Does Not Forgive (1968).
James Garner, Jack Elam, Harry Morgan, Henry Jones, Walter Burke, Willis Bouchey, Gene Evans, and Kathleen Freeman all appeared together previously in "Support Your Local Sheriff" (1969). Though this film is not a sequel to that one - all the above actors play entirely different characters in a different town - they all played similar characters to those they play here.
James Garner's line, "Patience, there are some things a man just can't ride around... but then again, maybe he can," is a parody by screenwriter Burt Kennedy of a line he wrote, more seriously, for two Burt Boetticher westerns starring Randolph Scott, The Tall T (1957) and Ride Lonesome (1959): "There are some things a man can't ride around."
It is a bit of a technicality the train seen at the beginning and end of the movie was not the Durango and Silverton it was still the Denver and Rio Grande Western. In 1971 the DRGW was still owner and operator of the line and this trackage was still part of a class 1 railroad and not a tourist / heritage railroad. Even though DRGW was looking at the time for a buyer or just the permission to the interstate transportation board for abandonment of the rail grade. They would find neither until the mid 1980s.