Ingredients: Beast Wars Optimus Primal and TransMetal Optimus Primal.

Basically all I did was take the screw from the back of the heads on both figures. (On TransMetal Optimus I removed the brown "Robot Mode" head.) I was lucky that the heads were swappable.

I had to trim down the pegs in the "ears" on the inside so that everything would fit properly.(Don't cut them off, just trim down the part that goes inside just so that it fits.)

I also installed them backwards to make it look a little bit better, in my own opinion.

He is still completely transformable, though I didn't post any photos of him with his original blue head because, well, that would have been redundant. But the new advantage is that his new head can be used in both modes, as you can see in my epic dutch-angle shots. This could still be done with his original head, also.

All in all, this took maybe about 10-15 minutes, done on the fly where I bought both figures.

And he still retains all the same articulation as the original TransMetal Primal. GO FIGURE! (Pun intended.)