I agree with McGyver. I would drill 3 1.75” holes for the drains for 1” bulkheads & use a 3/4” threaded bulkhead for the return. If U use a 3/4” threaded bulkhead for the return u will be setup for locline if that is the route u choose. The locline adapter will screw straight into the bulkhead, so u won’t have any adapters u will have to use.
That is how my 40 breeder is setup. A internal overflow box that I made 28” long, 3- 1” drains for a beananimal drain & I have a 3/4” return drilled on each end of the tank. That is why I only made the overflow 28” long is so I had 4” on both ends for the returns.
As far as hole placement, I drilled the drains 1.75” from the top of the glass to the top of the hole & left 2” inbetween holes. I stayed the minimum recommended distance from the top of the tank because I wanted the overflow box as small as possible. The lower u drill the holes the taller the overflow box will have to be. Drilling the holes where I did I ended up having to make the box 28” long, 4” tall & 3” wide. I also used smoked glass & schedule 80 90’s inside of the overflow to make it less noticeable. The sch 80 is grey instead of white.
Here is a photo, it really isn’t that noticeable
