The KC has a full lug under the barrel and the Trooper Mk. V does not (only an ejector rod shroud) so the Trooper would probably fit loosely in a KC holster and the KC will be a little snug (or won't even fit) a Trooper holster.
When Colt decided to bring out a lower cost service revolver in stainless steel, they simply designed a lugged and ribbed barrel for the Trooper Mark V and changed the metal to stainless.
Since many holsters are not molded that closely around the barrel, and other than the extra length of the King Cobra under lug there's not that much difference between it and the Trooper Mark V barrel, so they will likely fit the same holster.
You just caused me to produce a question.
You're more experienced with the Troopers than I am. I need to pick up a few spare parts for my MKV, would you say King Cobra stainless internal parts would interchange?
The hand's a little funky looking on this one & I'll be looking for four or five spares shortly, among other things.
Hammer & triggers interchange?