I would put the second hole next to the existing one and same height then adjust the PVC height wherever you want the water level to be, of course the overflow box here would have to be at the right height as well, beauty with doing this on glass is you can redo the silicone if you get it wrong the first time.
An overflow box in this context would be a very very strong recommendation because with this design now you will be staring at PVC plumbing sticking out of the back of the tank without the box. To answer your question more directly yes it can work without the overflow box but it can not work without the PVC 90 elbow & piece of straight PVC pipe sticking up from the BH, that's the emergency pipe, the full siphon pipe would have to be a 90 elbow pointed down, some people point them facing downward at a 45 degree angle because when the pump comes back on it will achieve full siphon more quickly. All of which would be visible without a box.
The durso part of your drain would have to go, you would have 90 elbows on the inside & outside so essentially your full siphon tube is doing an upside down U through the back panel.
I'm drilling mine as high up as I can go that way I can have the shortest overflow box possible, I'm going to try to pull off 3" from the surface & 3" from the back.
I too plan to angle my full siphon elbow at 45 since the bottom of it will practically touch the bottom of the box