OK, here is the skinny on how to remove a blown case from the 5.45x39 ak74.
Go to a Harbor Freight and get a complete tap and die set made in china for $9.99 and take the SAE 3/8X16 tap and use it to remove the case.
You need a real small 1/4" open end wrench to turn the tap. It is not real difficult to get it to thread but you have to keep it straight into the case so as not to scrape the side of the chamber. I used a medium size screwdriver to keep the tap straight after just getting it starten into the threading.
It only took me about a half to three quarters of a turn to have enough bite on the case to tap it out with a cleaning rod.
The hardest thing was finding a cheap tap. Maybe they could be picked up at a swapmeet or flea market so you wouldn't have to buy the whole set. Most tap and die sets at auto supply shops run about thirty bucks but the cheap china set works for this task really well.
Hope you don't have to do this any time soon.