Cool guys, I already ordered two 12" fans from Serban, so we'll see how fitment is when I hook 'em up. If I only have room for one, I'll either sell the other, or keep it as a spare.
Thanks again for the advice.
And Sneaky, There's not many faults that could cause your fans not to kick on. Worst case scenario, just wire them to a switch and turn them on manually, until you diagnose the real problem.