Here's my last set of the conversion kit for sale. This includes the magwell that takes AR mags, fully lugged bolt that works with both G36 mags and AR15 mags (and still works with SL8 mags also), and also original spec gas piston that satisfies US parts count.
After you widen the SL8 receiver internally, this set will allow the use of AR mags. And coupled with a G36 magwell, it'll allow the use of G36 mags as well. Selling as a set for $350, plus $5 shiping, or will trade for AR barreled M4 type upper.