Do you have any pics of the original Centurion design?
*rummages*
Just some very shaky pictures from a Games Day in 2004 - first ideas for something that in the end never surfaced. The Centurion of today is much bulkier, but I think you can see how they could be influenced by the older designs:
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I guess I like the Centurion well enough, though I would have fluffed it differently (basically a "Terminator -1"; an awkward hybrid between PA and TDA meant to counter the Imperium's loss of knowledge in regards to Termie production).
And BA and Necs fist bumping and rolling out without another shot fired. WHAT?? WHAT?!
As much as this is internet hyperbole, I admit I did not find that very fitting either. I could see a temporary alliance between those forces - but it would only be 40k if each side attempts to wipe the other out after they're done with the common enemy.