While I know it's not entirely an original idea, I've been pottering recently with the idea of making my Fusion Scorponok/GF Megazarak into a Headmaster. I looked at potential kitbash material, mostly spare Minicons like Rook and Crosswise, but mostly drew a blank. Then I came up with the idea of scratchbuilding it.
I've drawn up a few sketches of how I intend it to work. The general principle is that of a G1 Headmaster figure, only scaled to fit E-Scorponok, and with better articulation.
One of the sketches:

I've started with the face, which will also form Zarak's back piece.
Here's the piece so far, Blu-Tac'd onto Scorp's head. It's literally just constructed using layered pieces of sheet styrene. The brow piece, which will form the hinge that lets the crest cover the face, is a piece of small styrene tube.