I heard that there are "detachable" sks mags, but are they truly detachable, or do you have to take your sks apart to remove them (they have duck bills, I think)? Are there any kits I can get to have detachable mags without any gunsmithing? Oh, and if I win the 10 or less game, can I put a folding stock on my sks? I want to do that but mine's all original parts....
The duckbill mags are detachable, but reliability is kind of an issue with most of them. If you reduce the number of foreign parts on the list of 20 to 10 or less you can do whatever you could do with a US made gun be it adding detachable mags, or putting a folding stock. This is the case regardless of whether you want to use the SKS detachable mags or convert the gun to take AK mags.
Converting the gun to take AK mags has some pitfalls. First off, although it's technically possible, you'd have to be an experienced gunsmith with access to a machine shop to do it. For all intents and purposes, it's not possible for the average person to make such a modification, despite the fact that there are plans for doing so available on the net.
Secondly, the US made SKS detachable mags are usually an integral part of the plan in reducing the number of foreign parts. A standard SKS mag counts as two foreign parts (mag body, mag follower). SKS detachable mags as well as AK mags count as three parts (mag body, mag follower, mag floorplate). All SKS detachable mags are made in the US though, so by using them, you're reducing the number of foreign parts by two. Since most AK mags you're likely to get are foreign made, by using them you'd be adding three foreign parts meaning you'd have a net gain of one foreign part.
The above situation would be ok if you'd reduced the number of foreign parts elswhere, but there currently aren't enough US parts being made to keep it legal. You'd have to manufacture your own fire control parts to be safe. Bear in mind It's entirely possible to have a gun that is in compliance until you insert the magazine, at which point it becomes an illegal configuration.
Remember, the 10 parts rule doesn't apply to just any parts, there's a specific list of 20 parts that count (not all of which an SKS necessarily has). Of the 20, the ones that would apply to an SKS are as follows:
Pistol grip (if you add one)
Muzzle attachment (if present)
Of these 18, if you reduce the number of foreign parts to 10 or less you can add all the "evil" features you want.
edit to add:
In answer to your other question, the duckbill mags do not require any kit, If you remove and reinstall the trigger group without the standard magazine in place, the duckbill mags will drop right in, though some of the metal ones require some fitting. Some kits exist to use special mags without the duckbill, but these may require some gunsmithing.