The magazine adapters just bolt onto the bottom of the SKS action. With the magazine adapters, you hack the duckbill off the front of the Tapco 20-round magazines. The 5th generation allows the modified magazines to drop free when you press the trigger-shaped catch, if your bolt is modified so that it doesn't retain the magazine by the feed lips. The magazines go straight in, with no rock-n-lock.
The 3rd generation magazine adapter allows for trimming the duckbill off the front of the Tapco magazines, but the adapter is really just a front lip for holding in the front of the magazine.
For use with stock rifles and the 3rd generation mag adapters, they also have an extended magazine catch. It's hard to tell from the photo, but the catch is sitting right in front of the trigger guard.
The mag release is pretty expensive though, at $58 (shipped). They will send you $7 through PayPal if you send them your stock SKS mag catch though. The 5th generation mag adapter works out cheaper than the 3rd generation adapter and extended mag catch.
They say this stuff will work with ALL SKS rifles, regardless of which country they're from.
I think there will be an SKS rifle build in my future. I'm thinking a 16" barrel (or maybe a 14.7" barrel with permanent attached flash-hider/brake), 5th generation mag adapter, folding stock, scout scope base. . . Sounds like a lot of money to put into a $300 rifle, but have you priced AKs lately?