Many months ago I started out building a 74 in a .223 caliber. I finally got some of the items out of the back log and had time to work on the beast.
I started with a AK-74 Bulgarian kit from K-VAR and a .223 barrel from them as well too.
If you can do a search in here I posted some info on the trunnion size and dims of the barrels.
If I do this again I will start with a .223 blank and contour it my self. The location of the gas port is .100 inches too far forward. And some of the diameters were too large and needed to be turned down a bit. I set my barrel back and re-chambered. Rechambering is a bitch on a chrome lined barrel. I also silver soldered the FSB .100 forward to comply with all laws.
Everything was pretty simple after fixing the barrel. The 74 bolt works no problem with the .223 dia head.
The 74 mags I'm using are double circle 21's. With a slight lip tweak they feed with out a hiccup.
Personally I would not recommend this conversion to the causal DIY guy. The barrel took a lot of machining to get it to fit right (were talking mill and lathe). If I had some CNC equipment Ill bust out some barrels precontoured. But sadly I don't.