The SKS is a decent enough rifle, but it's not God's gift to the rifleman. And it isn't exactly some sort of rare, prized piece of history either.
Swapping stocks takes all of 30 seconds to accomplish and the Tapco T6 stock is a very nice option to have. If it makes the rifle fit you better, there's no reason not to use it.
The fixed 10 round magazine works great, the Tapco 20 round detachable also works great. There is an old, no longer manufactured USA brand 30 round mag that also works very well, but they are so rare that it's irrelevant anymore. I wouldn't mess with any other magazines.
One real important note, and that's 922r compliance. If you swap out the stock on the SKS you'll have to replace a number of other parts to keep it legal. This is where a cost:benefit ratio comes in to play. If you really like the rifle, then modifying it is probably worth it. If it's just a plinker, then the cost is probably not worth the benefit.