Well- I heard back from Steve "Chow". The Eurobraces on the 150 are: and I quote
"They are 2-1/4" wide. And the front and back braces are 7/8" down from the top and the side braces are 3/8" down."
He did not tell me how thick they are - i re-emailed and asked . I am now re-designing the internal overflow as our measurements were apparently incorrect - hmm.. Soul- I looked at your pic and it seemed right on at 1/2 inch from the top, and 2.5 inches wide.
I am now thinking about making the overflow be a horizontal gap between the Eurobrace and the internal overflow box with the front panel of the overflow box angled backwards. Because if the Eurobrace is 7/8 inch down from the top of the tank and it is 1/2 inch thick = 1 3/8 inches. So, the best any vertical ( parallel with the front edge of the Eurobrace) can result is a water level that is 1.75 -2.0 inches from the top of the tank. However if you make the gap horizontal with the Eurobrace - then you can have your water level at 1 3/8 inches from the top of the tank = much better.
* I had no idea I was creating such a issue by not wanting to use the stock middle tower overflow.