There's a list here of movements in various watches on the Orbita website.
I have no idea if it's accurate or not but I noticed something that made me curious.
Here are the entries for the Ball Hydo GTM's:
Engineer Hydrocarbon GMT I Ball Caliber 2893-2
Engineer Hydrocarbon GMT II Base ETA 2893-2
I'll bite - what's the difference in the Ball Caliber and the base ETA? If you know, pls be as specific as possible!