"SonomaProducts.com" writes:

Well with a lag you could do a 1/4" counter bore and the head would
then sit under the surface and still have 1/2 of grab. That's plenty,
but two deck screws at each stud will be just as good I suppose.

Here is a link to what I call table irons. Its an old term from
original Stickley days, maybe outdated now. http://www.rockler.com/product.cfm?Offerings_ID=786.
They have an info sheet on how to install. I use a Forstner bit and
make a round rabbit that hangs partly off the side of the table apron
(or ledger in your case). But you can use a squared cut-out just as
well.

If you are worried about sag, the sagulator says that a 500 lb center
load will deflect (sag) 1/16 of an inch.


And I believe that is without even taking into account the cleat on
the back wall which should significantly reduce the effective span.