Capn-
Thanks, that is really helpful. I read all over the place about how easy it is to create monsters and NPCs for 4e, but still feel like I do not quite grok how it works (despite having re-read the DMG pages several times). I think you nailed it: I am looking for a "conversion tool" where one does not really exist. Similarly, I am expecting to rebuild 1e NPCs in 4e terms, but that might just not make sense.
I started by using PC design rules to make real "conversions" but quickly realized that was a waste of energy, because the resultant NPCs are literally too detailed to be useful (with extraneous powers that exceed the number in NPC guidelines).
OK, so let me try a real example. I have an orc witch-doctor in the original A1 module (dungeon room 16 for anybody interested). He is a cleric 3/magic user 3 in 1e rules. Where would I start with this guy? Should I look for "orcs" from MM? Or maybe start with "cleric" NPC and add some orc traits and/or wizard powers? Are there any guidelines for which power levels are appropriate to swap?
No real guidelines other than "attack, hp, defenses, damage, etc" should all stay within a certain range or average for its level.
Using your example...
First, I'd try and figure out what 4e level it should be (what level are the PCs supposed to be for the module? And is that orc supposed to be a super tough monster for that level? Or about the same?)
Then I'd figure out the role (from the monster roles)
Then I'd figure out which monster fills that role, within 2-3 levels of your level target.
Then I'd adjust level up or down of the 'similar' monster to the target level
Then I'd reskin it to an orc, reflavor any of the powers, and maybe swap a power if you feel it still lacks some 'trick' that you want it to do.
So (i'm making up numbers here)...
Let's say your orc witchdoctor should be level 4. And that you want it to fill the controller monster role. I then flip through the MM and find the Goblin Hexer (mmp137) to be closest to what i want.
So I level it up one level using the DMG guidelines (which means the defenses and attack each go up by one, hp increases by 8, and xp goes up to 175).
I then reflavor the goblin to be an orc, so i remove the goblin racial powers (goblin tactics) and replace it with an orcish racial power.
Then, let's say I also want a little more on the original monster's healing role. So I replace incite bravery (which wouldn't do anything since it's an orc not goblin now) with "incite courage" that grants 5 temp hp when an ally within 5 squares charges. - yes, I just made up incite courage.
And then any physical changes to appearance...
That's really all I'd do.. (or apply the appropriate template if i wanted to make it an elite monster).
moral of the story: you hit it on the head when you said you're looking for more formal rules where there are none. There are GOOD rules, but they are very free form rules that give you a lot of freedom.
Disclaimer: I'm not claiming the above is the best thing in the world. just was used as a quick and dirty explanation for what the OP is asking.
Edit: crud, I just noticed that there is already an orc that might fit what you're looking for - Eye of Gruumsh, MMp204)