Since we will grind or mill down a Yugo M70 stub to look like a flat AKM trunnion, that means that an AKM-style receiver is what is needed - not a bulged Yugo receiver. I like metalworking and have a lot of tools including specialty AK tools. Because of this, I decided to make my own receiver based on a standard AKM sheetmetal flat from AK-Builder (www.ak-builder.com) rather than buy one.
Building from a flat is not a cost-effective approach if you only want one rifle, thanks to the amount of tooling and experience you need to do the job right. There are people who like to prove they can bend a flat with angle-iron and a hammer; that's not an approach that I can recommend, but to each his own.
To be clear, it is legal to build your own receiver for personal use and only for personal use. If you sell the rifle, the ATF requires you to mark the receiver with your name, location and the serial number of the rifle. From a liability perspective alone, I would not recommend selling a homemade rifle.
For people interested in only building one rifle or not wanting to build the receiver for whatever reason, I'd recommend buying a standard AKM receiver from NoDak Spud (NDS). From a legal perspective, the ATF considers the receiver the actual firearm, so you will need to buy the NDS receivers and have them processed like a firearm by your preferred Federal Firearms License dealer. If you think you will sell this AK in the future, that would be another good reason to build on a NDS receiver.