The AK files is where all the builders hang out.
You're going to need access to a couple hundred dollars' worth of tooling, at least. The easiest way is to use Toth Tool & Engineering tools. Search Youtube for the "kitchen table AK build" series. The guy there uses Toth tools and shows you how to do it. That's about the least tool intensive way to do it.
Be advised, you will need a parts kit with an already headspaced US made barrel to do it that easily, without a hydraulic press or a good drill press. Kits with original foreign barrels WILL require the use of a drill press to remove their barrel pins. Don't try to punch or hammer it out. You'll just ruin something. I learned firsthand, then I bought a press.
AK Builder is an excellent source for flats and headspaced parts kits with new US barrels. You will probably be able to get the barrel pin out of one of those because it hasn't been stuck in there for decades and AK Builder probably lubricates them.
You'll need a jig of some sort to bend the flat. Then you'll have to heat treat it and there will always be a risk of warpage when heat treating. It can't be avoided. The risk is there. If you're dead set on an 80% receiver, look into Childers Guns receiver blanks. They're already heat treated and they sell some tools to help you get the holes drilled right. That would be cheaper as far as tools go and, IMO, would yield a better receiver.
Either way with an 80% build, you'll need access to welding tools to weld the lower rails to the receiver.
Or you could buy a solid 100% receiver from NDS.