Reference to North by Northwest is clear in bed scene Matthau/Farr when Matthau speaks of "south by southwest." Also, the cropduster harkens back to N by NW, notably the runs at person on ground.
Felicia Farr was well-known singer -- e.g., "Song from Moulin Rouge" of early 1950s.
Ending of film totally unbelievable, in my opinion.
I don't know if I would call the ending 'unbelievable'. Would you care to elaborate?
SPOILER
Varrick would have to known a few things before planning such a tactic, one is that the hit man Molly suspected an inside job (not too hard to guess). An two that he would be at the junkyard and be alone. These are fairly reasonable guesses, but his biggest chance he took was that Boyle did not have a gun with him (He could have asked Ms Fort if he packed) and that Molly would not force him to open the trunk (Probably why he said that his arm was broken).
Molly was have been suspicious of an inside job already, and when Boyle told him not to be at the junkyard this deepened his suspicion. So Mollys reactions is not illogical.
The only thing that would have really blown the plan is if Boyle told Molly to be near but unseen at the junkyard, where the 'We did it ploy' would not work.