Read this..... https://www.hkpro.com/threads/the-complete-reference-on-the-legal-nfa-conversion-of-hk-firearms.527798/
or recommend Reuben read it and answer your questions directly since you'll be paying top of the market and deserve answers directly from the seller if you pay those prices.
You should know HK's are not that "durable" in general, relative to other SMG's and they are relatively expensive to fix. I enjoy them and have well in excess of 10K in spare parts, but that doesn't even fill a small tackle box. Last week I needed a part and there are currently none for sale. I might end up waiting a year or more for a part to show up for sale. (a 3 round burst left selector switch) before that trigger group is completed.
Best of luck in your purchase.
