Tranny oil pan issues....

Ok, grabbed the 5/16-18 kit suggested, tap says use a 21/64 bit to drill out the threads. Bolts on the pan are 1/2", just want to make sure I'm on the right track before I do any drilling?
The bolts are NOT 1/2 inch
The heads are,but the threads are 5/16-18 as already stated.
Make sure you use the indicated size drillbit, and do not let the drill "waller" out the hole.