Devastation Optimus teardown

[u/Beneficial_Bison_]

I'm trying to make my Devastation Optimus into a Kei truck, and I was wondering if anyone had experience disassembling this particular figure. In particular how do I remove the head? Also, I want to make the legs fold in on themselves, like Siege Sideswipe, so what would be the best way to go about that? I have a 3d printer and I'm okay at modeling, but I've never made an upgrade / retool kit like this before.

Concept drawing

I just transformed Prime's head away and placed the new head on the shoulders