I would expect the loss due to the drivetrain to be MUCH greater than just 40HP. In fact, in almost every dyno we have seen on this site for the V6, the drivetrain loss for an automatic V6 is usually 20% or higher. I believe it is about 21% loss.
So using that estimate, if the car is truly making 405HP in 4th gear on the dyno, that would mean the car is really making about 500+ HP at the crank.
2016 Camaro 1SS - 8-speed - NPP - Black bowties
2010 Camaro 1LT V6 (Sold. I will miss her!)