James,

The stability margin for delta wings should be between 5% and 10% MAC.

If you enter the wing tips and tail area as zero into this calculator, you will get the exact location of the CG for any delta wing:

http://www.geistware.com/rcmodeling/cg_calc.htm#cg

Just for verification, if you enter the values shown in the second attached schematic into the calculator, you will get the same shown results.

You can find more information about balancing any model here:

http://adamone.rchomepage.com/index5.htm