Yeah, as he said it is not certain whether it will or not.
There is a good chance it will, and a good chance it won't.
You can always drop them in and see what happens. You might have to drop the speed down to 1333MHz.
If it doesn't boot there should be no damage to the system, just power off and pull out one of the sets.
If you do decide to drop them in, you will want to split it up like you said. 1&3, 2&4