Kevin, the 922-r regulation has to do with imported firearms; basically, it says that if you begin changing certain listed parts from an imported firearm, then you are "manufacturing" or "building" a completely "new" gun;
The "new" gun can't have any more than 10 of the old imported listed parts on it.
Depending on the origin of the SKS rifle, it has either 14 or 15 listed parts, as listed by the BATFE; Yugoslavian 59/66's have 15 parts, most of the others, including the Chinese, have 14.
Basically, you have to replace either 4 or 5 parts to be compliant; If you go to the threads at the top of the Legal Issues page, you will see a number of thumb-tacked "sticky" posts. Read through these, and you have have a much better understanding of this matter; they include letters to and from the BATF, as well as lists of the parts.
You will see that bay replacing the stock, upper handguard, and magazine, you have replaced 4 parts, and will be compliant in most cases; the other parts, like scope mounts, etc, do not count, since they are not on the list.
Read through that material, and I hope this helps.....