Colt Series 70. The trigger, ejection port and mainspring housing are more faithful on the 70 than on the 1991 series.
From Colt's website :
"This pistol features the legendary Series 70 firing system, making it a faithful reproduction to Government Models manufactured prior to World War II. This pistol also features an arched steel mainspring housing and a short steel trigger. A standard safety lock, standard grip safety and spur hammer complete this authentic throwback to Colt semi-automatics of days gone by."