It feels like the easy answer here would have been to remould Grimlock so he had a more Godzilla-y head and spinal fins, and then you could paint one black and give him a Megatron head and the other silver and give him an Optimus head and boom. Godzilla/Megs vs Mecha Godzilla/Optimus.
Beats just a straight repaint of Grimlock with a Megatron head and a truck mode Optimus who's just painted in Mecha Godzilla colours.
Beats just a straight repaint of Grimlock with a Megatron head and a truck mode Optimus who's just painted in Mecha Godzilla colours.