Looks to me like you could do the tenon with your router and the "mortise" with a saw and chisel. Those are big joints. You could even bandsaw the mortise since it's open ended or use a nice Japanese pull saw (c'mon... you know you want one) and then refine it with a sharp chisel. I think you'll spend more time trying to figure out how to do this with power tools than it would take you to just go ahead and dive in with hand tools
