Is it not turning over, or, is it not starting?
If it's not starting, is one engine from an automatic and the other a manual? The bank 2 cam gears have different relucter points for the cam sensor.
If it's not turning over, check the small wire on the starter and make sure it's connected proper. It may look like it slid on but not making contact on the solenoid.
If that wire is good, then recheck your battery cable connections, positive and negative, and that all the grounds from the harness are clean and tight.