It actually started out as a Big Der Red Max clone on E power. Instead of finishing it as D/E powered, I added 3 BT-60 tubes, with a separation in the middle coupler. Capped off the upper section (so less volume for the ejection charge to fill).
So, to do the same thing, you would start off with a Red Max kit (to get the fins, decals, nose cone). Probably easiest to buy a Mean Machine also, to get the 4 body tubes, and E motor mount. The new Mean Machine has a different twist lock center coupler. You could probably modify it, for center separation.
Then what do you do with the left over Mean Machine fin parts and Short Der Red Max body tube? Make a midget Mean Machine...with 18mm motor. lol