In a nutshell:
To convert published stats from D20 to Conan, you need to drop AC, calculate DR, Dodge Parry and Magic Attack Bonus. One of my docs has chart sfor that, but it needs revision. I put it on a GM screen panel so I can refer to it on the fly.
For monsters, increase hit die by one type -- d6 becomes d8, d8 becomes d10, etc.
To avoid having to rewrite every spellcaster in a published adventure into a scholar, I use the Grim Tales magic system. The Conan-modified version of that is also on my website. Cross off an spells that don't feel right.
Flush all magic items down the toilet.
Try to keep the number of sorcerers down to one per adventure -- use Fate Points to keep bringing him back rather havng five different magic-using bad guys.
All humanoids (elves, orcs, dwarves, etc) are humans.
I leave D&D classes alone, but while GMing refer to the character by the Conan equivalent -- you meet a ranger and I tell you the character has the air of a Borderer, fighters are Soldiers, etc. Strip out paranormal class abilities.
Keep monster encounters down to one supernatural creature per adventure. Usually demons or abberations. Replace all other monsters with animals -- lions, bears, snakes, whatever works in context. When I ran Necropolis, I replaced a pack of werecreatures with a band of thieves in masks pretending to be werecreatures, and freaked the players out.
Magical traps usually need to be replaced with non-magical ones, and some traps that seem too high-tech also need to be scaled down. If you've got a good book of traps lying around, bookmark ones that seem right for Conan.