I'd be REAL careful with this... A large, real large amount of torque taking place back there...that is/would be "out of balance"... That is a heavy boat, and the 150s each provide "focused" pressure on the "braket" rather than the transom areas to push the boat.
I will defer to the real engineers, and folks that may know the technical answer to this.
One afternoon on my TC24, with twin 90s, I wanted to know the same thing... Answer:... Well... if I was going down and needed to get to shore faster than 7 knots (which seem to be the highest speed mine would go without just feeling all bad and weird).....then I'd do it if the water was real cold or had more than me on board. But...just to possbily save fuel, I would not go there. Just too many things out of whack.
But then... my motors were mounted right to the boat... so... just how does or does this change with the Armstrong brackets? Hummm
I know it should not/would not take but about 50-80 hp to keep it on plane once on plane... but is it just too much twisted torque...?