A quick look over http://politicalgraveyard.com/offices/pdio3.html says nobody has died in office in a presidential election year in the last century, so the circumstance is itself unprecedented in modern times.
Anthony Kennedy was nominated in November 1987, and confirmed in February 1988 (he replaced Lewis Powell, who retired in 1987). So a couple months earlier, but still very much in an election year. If Saint Reagan did it, it'll be difficult for the GOP to make an argument that this president can't (even if you ignore that the constitution says he can).
