Boosted LS1

Hi, I've noticed that the GM main bearing shells have an 'odd' lower shell. The locating tab is in a different place to the other lower shells and there's a black identification mark on the rear of the shell.

Does anybody know why this is and if this shell needs to sit in a specific cap?

Thanks.

Boosted LS1

Got it sorted. The bearing with the black i/d mark is correct, p/n 12639738. It's the other shells which are incorrect as they're a different i/d, doh