Anybody have experience building one?  Do you have to use proprietary PSA parts or can you use anything as long as you have an upper and lower set? Any help or direction is appreciated.

I have one.  Their lower will take a milspec parts kit, minus the bolt catch and mag release.  The lower will mate with milspec uppers but ak magazines won't fit in those.  The ks47 upper and bolt carrier have a wider opening for the magazines.  I believe it came with different weight buffer and longer firing pin, too.  But I'd have to double check.  Barrel is obviously 7.62x39 instead of 5.56.

So far, they haven't sold a stripped upper.  You either have to buy a complete upper, whole rifle kit, or some people have got a billet upper from another manufacturer and had it milled out.

Billet Rifle Systems has a similar style system, however it only accepts AK mags. You can buy their upper stripped and mate it to a ks47 upper

I just called up Billet Rifle Systems and spoke with the owner.  He said that he gets that call a lot with people wanting to know if his parts are interchangeable with the KS-47.  As of right now, he is not sure.  Be has ordered one of their bolt carriers to try in his upper.  And sometime shortly he plans to be selling his own bolt carrier, which will be about the same price as PSA's.  One of the biggest complaints about the KS-47 is how there is nothing in place keeping you from pressing the magazine up into the rifle too far.  If you rest the gun on the magazine while shooting, the mag will interfere with the bolt carrier and cause it to not cycle.  I asked the guy at Billet Rifle if their version suffered from this as well and he said they upper has a tang built into the front/bottom of it to prevent the magazine from going in too far.

IMO, that would be a huuuuge win for this Billet Rifle upper.  The only complaints I've seen about the KS-47 are related to how the magazines fit with the bolt carrier and upper receiver.  If you could build on this Billet Rifle upper and fix those problems, then I say it would be worth the extra cost.

I bought the BRS47 upper/lower. The lower has metal piece that keeps the magazone at bay like the owner was saying. This little metal piece sits behind the front takedown pin. It's very well designed. I still am waiting for the ten day wait for California, but am picking it up sometime next week and will probably create a thread regarding my thoughts.

As for the carrier, I know a guy who slightly mills any carriers to allow for the AK mag clearance.