I finally got around to completing the project that I've been meaning to do for the last few years. I originally hacked up a VFC slide stock to fit the TW5 a couple years ago and then it sat. I recently picked up a G&G SD6 from a member on here and began the hack job of combining the two guns together. It was a pain in the ass. There may be a better brand to do the conversion, but I made it work. Overall, I'm quite happy with the way it turned out. It's solid and looks clean. I'll try to describe some of the aspects of the build but my MP5 terminology is lacking. I'll be making up names so just roll with it.
In the picture below I ended up JB Welding two halves together to make it fit right. I couldn't keep the Systema charging tube(?) stock and mate the sight post of the G&G without it looking like garbage. I cut both parts in just the right places then mated them together. You can sort of see a seam line where the tube tapers. I then repainted it. It was a hack but looks great now. You wouldn't know it if it wasn't pointed out.
In the next photo I had to enlarge the suppressor adapter so the inner barrel could get through. Looks nice and clean.
In this photo it shows the heat shield guard thing. In order for this to fit I had to remove some material from the outer barrel and the charging tube. Not a lot, but enough so the screw points could mate up. At the rear of the handguard, the TW5 is a bit big for the heat shield to tighten properly. I didn't care enough to start removing material from it. It's a touch wide but the ribbed(?) part slides over fine enough.
In this picture I'm showing an FCC positive to negative thread adapter. The TW5 is positive, the G&G suppressor adapter is negative. I didn't want to completely disassemble the gun for viewing pleasure but, I had to cut off some of the outer barrel end so that things would line up properly. The FCC adapter was perfect for this job. Thanks Tanner for having this kicking around!
Looking at the photos, things look pretty clean but the process was not. A lot of little careful work to make sure things lined/mated up nicely. Overall though, I quite happy with how it turned out and it's a rare piece for sure.
In hindsight, I probably should have documented this a little better. I'm not sure how helpful this is to anyone interested in doing it. Figure it out yourself!