I agree with Mil-Dot. I've owned quite a few Saiga's, converted almost everyone one of them. One was the .308 and decided one was enough, too hard to find mags and cheap ammo for. One was a .223...never again.
All the rest were 7.62x39s and all were great guns. Based on my experience, the x39 version is the easiest to convert, easiest to find mags for, and there's lots of cheap ammo for it. Barnaul/BrownBear worked well for me, HotShot wasn't bad, Golden Tiger was my favorite when I could find it. Wolf was most available but last choice is it was usually slightly less accurate and much dirtier ammo than the others.
So, do yourself a favor, get the x39.
Go to
www.dinzagarms.com and get your conversion parts.
and check out
http://store.carolinashooterssupply.com for more conversion parts and ideas.
One of the best front handguard with a tactical rail on it is from SGM Tactical, is an exact replacement for the Saiga handguard, fits perfectly, super-easy install and looks good too. Has tr-rail for stuff but still has an un-railed area to place your hand. At $85 or so may seem expensive but is worth every penny, very well made.
http://sgmtactical.com/index.php3?pageid=TacticalRails.htm
Trigger: use a Tapco G2 single hook. Many builders will say the double hook works better or is smoother, I've used both but the single is easier to install and unless you've been building/shooting AK's for a while, you won't feel the difference. Also, I'd recommend getting the Tapco axis pin retaining plate to hold everything together. Don't rely on the cheap little wire shepherds hook thingy. If you want a lighter trigger pull, Carolina shooter supply offers a 25% lighter hammer spring.
Good luck with your build.