I don't think the 39-AS model with the safety is even drilled for a receiver sight.
Williams does make a version that mounts in the scope mounting holes on top of the receiver.
This looks like the side mount 5D but instead of screwing to the receiver side, it screws to the rear scope mount holes.
Otherwise, it's the same as the standard 5D.
http://www.brownells.com/.aspx/pid=4...ECEIVER-SIGHTS