Which Head is Which?

[Blurr]

On a 2nd gen set of heads, how does one tell which head is which, the front or the rear.

I have an extra 2nd gen head and I'm not sure if it's the front or the rear. It was disassembled at some point so I can't tell which side it was used on but if the loosely placed cam caps are any indicator, it was a front head, but looking on the side where the cam caps are, I can see the two holes for the Cam sensor bolts, where it would be installed.

Are the 2nd gen heads reversible?