Used front sight with a non-standard, opposite taper - forget it - front sight alignment and gas port alignment are too important. Get another front sight - new if possible - and ream for a correct alignment/fit with the sight base "straight up" and aligned with the gas port. The front sight will probably not be straight if you jury rig it with straight pins, and the gas port needs to align properly, as well.
SAW Sales (Specialized Armament Warehouse) is Colt's Full Auto/Police distributor and they have new Colt parts and can do the job for you if you want to be sure it's right. CC
Colt, Glock and Remington factory trained LE Armorer
LE Trained Firearms Instructor