At the risk of answering a question that's already been answered:
For the SL8-4 to use G36 mags or AR mags with the magwell adapter, you need to cut out two tiny plastic tabs in the receiver, which is a pretty easy job, especially with a chisel. No further modifications will then be required.
Alternatively, if you don't want the AR mag conversion, and want to use G36 mags, you can leave the tabs in the receiver, and cut out the space that the tabs occupy on your G36 mags. Given the rarity and price of the G36 mags, you're better off modifying the receiver, since then you can use G36 mags or an AR mag well adapter with no further mods.
With the single stack SL8s, not only do you need to modify the receiver so that the magazines will fit, but you'll also need to replace the single lug bolt with a dual lug bolt if you want to use any dual stack mags (AR, G36, double stack SL8).
Hopefully this covers everything.