Originally Posted by
slustan
You're probably looking at much older colts. Most all colts on the market now have FA BCGs, .155 trigger/hammer pins, and no longer have the hardened steel sear blocks. I'm sure there still may be some older ones floating around. The only real thing to contend with would be recountoring the barrel and the 20" match target doesn't have a threaded muzzle so that would have to be addressed.
When it's all said and done, my opinion, for what it's worth. Grab a bcm 20" w/ a bcg and GF charging handle and throw it on an a2 LMT lower and call yourself good to go.