When I first took an AK apart I saw all the machine marks from dull cutters and thought, "Man, why didn't they just do all these parts as investment castings?" Darned if I can find any sprue marks anywhere on the parts I have, nor can I come up with a reason why they'd duplicate such cobby machine work. If all you have to do is one part for a pattern, why not make it nice?
I have a milled receiver on hand, and it looks for all the world like they took a Big Chunk O' Steel and whittled 90% of it away. WTF? No wonder it looks like the cutters were dull...
Oh, and for something practical - if you build the back using a narrowed AKM rear trunnion, you can use AKM stocks if you narrow the spigot slightly. The selection of fixed stocks to fit the Yugo receiver is small, and prices are considerably more than AKM stuff. And Yugo trunnions are expensive, too.
I love the looks of the Yugo underfolder, but I just couldn't come to terms with the idea of firing a big bore cartridge with a T-shirt and the Yugo's horseshoe-shaped buttplate.