This aircraft (Boeing 727-051, serial number 18803/line number 137) was actually first ordered by United. Instead, it was delivered to Northwest, as N407US, on April 22, 1965.
Northwest changed the registration to N467US, it's registration during the Cooper hijacking.
Piedmont Airlines bought the aircraft on June 6, 1978, and changed the registration to N838N.
On December 1, 1982, it was leased to United technologies, and returned on February 1, 1983. It was leased again to Flight Dynamics, who used it for HUD (Heads Up Display) testing,.
The 727 was sold to Key Air in September of 1984, who registered it as N29KA.
It was finally sold to World Corporation Leasing in July 1988. It was then flown to Greenwood, Mississippi and scapped by the Memphis Group in 1996.
Tom in NO (at MSY)
P.S. Above info stolen from the November/December 1999 issue of Airliners, which has a good article on the hijacking.
"The criminal ineptitude makes you furious"-Bruce Springsteen, after seeing firsthand the damage from Hurricane Katrina