Screws 1-1/4" long.
Pocket hold drill guide---set for 3/4" stock.
Drill the pocket holes in the 2x4 stock.
Route the screw thru the pocket hole into the 3/4" material.
PS---get that job done quickly and head to Saguaro Lake for some crappie fishing.
I assumed that the pocket hole would be drilled though the horizontal 2x4's by using a Kreg Jig depth setting of 1-1/2 inches - which should result in the screw coming out at the center of the top of the 2x4.
Set the drill bit collar for the same 1.5 inch depth - so the drill tip just barely does NOT break through the surface of the 2x4.
The uncertain thing for me is exactly what screw length to use that will avoid it breaking through the top of the 3/4" table top. I think the best is to do some testing on scrap wood starting with using a 1-1/4" long screw, and then use a longer or shorter screw, depending on what your results are. If you run into troubles you may need to create a 1/4" plywood shim between the 2x4's and the 3/4 inch top to prevent the screw from breaking through.