F150 engine not the same as SHO/Flex/MKT/Explorer engine.
No, 400 whp is not the absolute max on stock block for the transverse, but it is closing in fast on the max RECOMMENDED level for a daily driven vehicle. I think a few have pushed it to 450 or so, the torque is usually around 500 wtq at that point. If you only run it on weekends, you can go for higher power levels. Expect special operating conditions-level maintenance tho.
I am only spouting generalities. Your tuner will be able to give you a better, more exact number.