The best tutorial was lost when the site it was on changed.
Basically, you center punch the rear trigger guard rivet and carefully drill off the rivet head.
With the head off, you use a punch to drive the rivet through.
Personally, I'd remove the rivet head on the outside of the receiver so the trigger guard isn't damaged when the rivet is driven out. It's easier to drive the rivet into the receiver.
The tang will, or should already have the holes, so you just use it as a drill guide for the rear hole.
You can either rivet the the front of the tang to the trigger guard and receiver or use a small bolt, then drill the rear hole using the tang as a guide.
You have choices on attaching the tang.
One is to rivet it, which requires a riveting tool that actually squeezes the rivet to form a tight head. It's difficult to get the rivets tight by hammering them. Some of the AK builder's site sell riveting tools or show how to make them.
Another option that works well is to use small button-head cap screws and nuts. With a little Loctite Red, these work very well and make a really tight mount of the tang. The nuts go inside the receiver.
All that's needed is to make a small clearance cut on the stock's socket to clear the rear nut.
Another and even easier option is to buy an Ironwood Designs stock that's made for the Bulgarian receiver with one tang.
This uses a through-bolt similar to how a shotgun uses a bolt through the butt stock.
Ironwood is top quality wood, and his Bulgarian stock looks good and is very strong:
http://www.ironwooddesigns.com/IWDsite/IWDHome.html