No, the 6400 is not an exception. It uses the oversize fire control parts. It *does* come from the factory with a standard-size captive push-pin for the pivot pin, which is good. Of course, any small-hole Colt can be converted to this configuration, though some will need the detent channel to be drilled, which is something best left to a gunsmith if you don't do that kind of work on a regular basis.
-Troy