I initially flipped the bench upside down and tried knocking the legs upward with a 5lb hammer, but they didn't budge. Since that didn't work, I flipped the bench back over and then put it up on my tall saw horses so that the legs were dangling up off the ground. This allowed me to hammer downward and use a lot more force. In this position I was able to use my sledge and after some good solid blows, I was able to get all four legs out.
Before I knocked the legs out, I used the bench to prepare the stretchers, which will connect the legs down by the floor. Each stretcher will consist of two 2x6's glued together with one being longer than the other to form a tenon that will go into a leg. I used standard home center fir 2x6's and after drying in my basement for the last few months they had cupped quite a bit. To be able to glue them together I had to do a good amount of planing to get them flat and straight.
One 2x6 was a little longer than the other, which when glued together created a natural tenon.
Once again I used the process of using the auger drill bit followed by a mortising chisel to create mortises in the lower part of the legs where the stretchers will be located. These mortises actually intersect on the inside, allowing the tenons to go as deep into the legs as possible.
Once the mortises were cut, I put a 45 degree cut on the end of the tenons and then trimmed them to match the height of the mortise.
I'm starting to see the daylight at the end of the tunnel on this project and I'm looking forward to actually putting this bench to work.