A V-104 is what you get when you mix a V-2 with an F-104 Starfighter. (Refer to the attached photo) On top is one of the pods from my rekitted F-104 Starfighter. On the bottom is the rocket being made from the other pod. The fins are spares from a Semroc V-2 (2 sets of fins were provided in each kit).
I whacked the top and bottom of the pod off with a razor saw. After a little grinding, a BT-20 fits nicely. To my amazement, I didn't have any raw BT-20 larger than a typical motor mount. I did, however, find an assembled long motor mount. It includes a thick cardboard thrust ring which can be seen on the base.of the body section. To attach it, I merely wicked some 5-minute epoxy into an existing slot in the center of the pod. This hole will be fully plugged and will be covered by one of the fins.
A BT-50 coupler fits the nose cone section and top of the body perfectly, so that formed the shoulder.
The pod is generally the shape of the Semroc V-2's tail cone as evidenced by the fact that just a tad of sanding was required on the lower root of the fins. I papered said fins and sealed the edges with thin CA.
This was built on the fly and I haven't simmed it yet. Hopefully it isn't too heavy for a C6 after I add any required nose weight. I don't know how I'll paint the fins. Matching the yellow plastic will be tough so I'm leaning towards just painting them flat black.