Back Seat Swapp

[TalonSway]

So im done with my interior swap but i ran into the problem that the leather back seats that i got is a 2 piece and i pulled out a 1 piece back seat. So my question is do i drill a hole? to hold them down i dont know what is down there under the back seat i dont wanna drill into my gas tank or anything. Any suggestions or know what i should do much appreciated!!
.. Sorry last picture of my old back seat is upside down.

 

[Jeff99GS]

I would take a piece of 1"x1" angle iron and weld or bolt it across the two outer brackets that can then be bolted down to the car with the two outer bolts.

I drew a Crude picture, the RED line is supposed to be the angle iron.

if you can weld, you can tack on some studs to Bolt the middle brackets to the angle iron with.