You can do it yourself no gunsmith required, no real experience requires either and it will take less then 5 minutes watch this video tutorial on youtube.
https://youtu.be/x-KI5JNmvWw
There is also a good video by sootch00 where he goes over the rifle all together but doesn't do the mag swap, the first video covers may swap though
https://youtu.be/6PLBejrF1CY

I avoid promag mags like the plague over 75 % of the promag magazines that I have purchased do not work

Like the above persons stated, this can be performed by yourself with the proper tools and know how. Knowledge easily obtained through social media.
Although no longer owned, I have owned an SKS and shot several, super fun guns! Adding a removable magazine does come with its pros and cons. Obviously, capacity will be improved. One can argue reloading speed is increased, however, its not intuitive, and, depending on how its installed, the magazines used and the user, it can be a more awkward and cumbersome procedure than using stripper clips.
On the other hand, reliability can be affected, as changing the firearms intended feeding style can inherit issues, feeding issues being the most common. Additionally, although not a collector rifle in comparison to military surplus rifles, but more so collectible than how they were viewed 10+ years ago, alterations can devalue the weapons, be it from non "OEM" parts or damages and marring due to enhancements.
That said, have fun, shoot well and good luck!

Jimmy, it is easy if you take your time and follow this video carefully. You just need basic tools and a few minutes : -- youtube.com/watch?v=pbiRnHlObqs