The abdomen on the Galbaldy-ß kit is your basic front/back/skirt armor assembly, leaving no articulation in the waist. And it's pretty plain looking proportion-wise. I decided this was a good place to begin, and started chopping things up, not sure what I would do to put it back together.
I knew that I wanted to try to add some articulation to the waist, so the first thing I did was to cut the chest away from the abdomen with my trusty exacto. I gradually scored along the edge of the abdomen until the plastic was thin enough to snap off. I also thought the whole chest looked too flat, so I used a razor saw to cut of the sides of the front piece, which would allow me to "beef up" the sections individually.
I then proceeded to bulk up the two sides of the front chest part, adding triangular strips of sheet styrene to the bottom and inside edge to create a new profile, and used thick C/A glue mixed with corn starch to blend in the new edges. This left the outside shape the same, while thickening the inside (where the center piece attaches), making the whole chest area less boxy. Since the left side had a recessed section (the cockpit?), I also used a piece of sheet plastic to cover the hole before filling it. Then I attached both reshaped parts to the top chest/neck part before reattaching the center (this made sure everything still matched with the back piece of the chest). The picture below shows the two side pieces (one filled, one not) attached to the top.
After I verified that the front still fit the back, I reattached the center of the chest. The curved part at the bottom didn't match the reshaped sides at all, so I built it up using epoxy putty (Ace hardware brand, no need for fancy stuff here!), and used Bondo orange spot putty to blend everything together.
Since I needed two of these modified chests, I had to design the parts so they could be cast in resin. That meant filling the back with something so I wouldn't be casting such thin parts. I plugged the bottom with a sheet of plastic to allow me to fill the chest front with Bondo polyester putty. I also needed to keep the cutouts where the polycap that holds the arm attaches between the torso halves. I temporarily attached sections of square plastic rod to the inside of the cutouts, to be removed after filling with Bondo. After I filled it with the putty I removed the plastic and ended up with a nice solid (and heavy!) piece.
The same procedure was used to fill the back of the chest. I also cut some bumps into the bondo on the front part to key it to the back when attaching the two halves, and cut a half circle out at the bottom to accommodate the ball joint I planned to use to attach the chest to the new abdomen I would build.
Having re-proportioned the chest to my liking, I just needed to add some details that were lost during the construction. I used the "Bondo squish" technique I came up with working on my Hi-Zack to replace the archway shaped details (verniers?) around the base of the chest. First I created a negative of the archway shape (cut out of sheet plastic), beveled it a bit with sandpaper, and glued it to a larger sheet of plastic. Then I used a routing bit in my Dremel to grind a recess into the plastic, filled it with Bondo polyester putty, pushed the negative shape into the Bondo while it was still soft, then pulled it out when the putty hardened and sanded the surface smooth. This was time consuming, as I had to make 10 of these all the way around the chest.
The cockpit hatch (at least I think that's what it is) was simpler, made out of sheet pretty basic sheet plastic. For the two oval shaped cutouts in the corner, I cut oval shaped holes in a very thin plastic sheet, then glued it over the top of the main hatch part. The side was made wit pre-scribed styrene sheet, framed with thin plastic strips. After I glued this in place I sanded the edges a bit to round out the shape.
Below are some pictures of the finished and primed chest, which also show the large ball joint I installed at the bottom. I'm very happy with the result, much less blocky than the original.