Ken, nice PPS43, produced in 1943. you were right, it's early gun.
bottom part with handguard is not original for this gun, it was replaced. Kulakov's factory was the only factory, where were produced guns with so called "early type" of safety, through trigger guard, so it should be on your example, but we don't see this.
All other 5 factories produced (even another 2 in Leningrad) guns with safety at the right side of trigger guard, as on your's example.
I have write article about early PPS, but unfortunately it is at russian languge, so I can't post it here.
Curved part at the stock is most typical to later PPS43, but sometimes could be seen at the early guns. Most possibly in such cases stock was replaced later
You mention poor finish... Sometimes in Leningrad because of lack of chemical components for bluing, guns were covered with a mixture of soot with glue.