Hi, i have had a lot of fun... Remolded the whole chest, opened the claws and added an extra articulation on the rear windows to move them to the upper leg:
The chest moldings are reeeeeeeally thin, from 1 to 2 mm in thickness, the forearms leave almost no room for anything extra in alt mode. I suggest molding first without worrying about thickness, and from then, keep on sanding until the forearms slip nicely over the the chest. The head was remolded after the artwork circulating on the web, based on the movie appearance:
For the legs, i cut the rear window just below the tail lights, and added a double swivel articulation, bonded to the inner thigh and the base of the window, thus allowing it to go up to the hip level, just as in the movie. The mudguards are made from the halfs of a soy sauce bottle cap. In order to add extra structure on the legs, you will have to carve the rear part of the thighs:
I found out that there is room enough to open the claws in a "3d" way, instead of the flat configuration. The wips are made from shaved pipe cleaners, which are flexible and thin:
Would you ask me, does it transform?

- Hell yeaaaaaaaahhh!!!!
The only visible differences are the new seam lines under the tail lights, the wips showing through the side windows, and the swivel articulations from the bottom:
Thanks for watching!