Once I figured out how to pull Brawl apart to get at his neck this was pretty straightforward (I'm not sure if I reassembled him wrong because I swear his stomach could go up further).
It's a repainted WFC Brawl with a modified CHUG Wheeljack head
https://i.imgur.com/GztUUEt.jpg
https://i.imgur.com/itF0I5R.jpg
https://i.imgur.com/ZTxK8P2.jpg
https://i.imgur.com/DxySMuN.jpg
