I am NOT trying to stir up the debate about MIM parts here. That one has been done to death many times over, let's just accept that the two camps have their opinions and are not likely to change.
My simple question is, though, can you put a new MIM part in an older gun? In my experience, the older hammers and triggers were basically "drop in" (of course they had to be checked for safe function.) Does this still hold true, or have things been completely changed?