Thx for the kind words people.
urgaffel: Yeah I've sorted that out now thx, added some extra faces in. I was planning on making the material in Unreal double sided but realised marmoset doesn't support this and also the inside needed capping anyway. Had to lose some bolt meshes to accommodate this.
Theht: I'll post some maps later on when I'm done texturing. I decided to unwrap one half of the body and mirror it, which is why I had to test it out in UDK & Marm. I wanted decent resolution because it's so large and also because I'm going for a fairly clean look it didn't warrant unique sides.
Here's a screenshot of my 'exploded mesh' bake setup in Maya for Xnormal:
Also I followed this
technique for getting more out of the AO in Xnormal & photoshop, it's subtle but brings it out and makes it pop which is nice. (Half way on the page, the bit about Cavity Maps)