The short answer is yes they can be fitted and usually drop in.
The long answer is they don't usually need fitting and have about the same success rate without needing fitting as swapping forged triggers in pre MIM guns, about 95%. Recognize that the MIM trigger was originally introduced and used with forged hammers for about a year (varies by model of gun) before the MIM hammer was introduced.
The trigger sear will almost always fit the hammer notches and DA sear. The only other rare situation is improper fitting/operation of the cyl lock stop.
Finding a forged trigger would always be my first choice, but not necessary. Of course if the MIM trigger width of .312" - .320" is the purpose of the swap, you'll need to find a forged .312" - .320" smooth trigger that became standard in the early 1980's (when all .500"/.400" K, L & N target and combat triggers were discontinued), and before the MIM triggers were introduced ~ 1997.
Which trigger does the K frame have in it now?
Hope that helps,