There are several problems with your request.
It's a lot more than "bolt(ing) together" parts.
Tommybuilt conversions take the rear section of a G36 receiver and "graft" it on with industrial polymer adhesives.
The difference between an SL8 receriver and an XM8 receiver are even greater. You can't simply convert a standard G36 to XM8 configuration, much less an SL8. The upper carry handle and the handguard, which are both integral to the receiver, are completely different. On that note, when you look on the Tommyhuilt website, their XM8 conversion involves completely recontouring the receiver profile, and using parts of an XM8 kit. Keep in mind this is work by someone who specializes in HK conversions and works with that kind of polymer.
Your last problem is sourcing the XM8 parts to even do this with. Last time I saw XM8 parts for sale, they were extremely expensive. I believe Tommybuilt is making kits inhouse now, but they're about the cost of an SL8, and good luck finding one in stock.
If you can find a kit, get IRG to bring it in, and find a smith that can do the work, which are extremely few and far between in this country, you'll be looking at over 6K in the rifle at least, and I doubt that you're interested in that considering you don't even want to have the barrel reprofiled.
