Will power be enough though?

Assuming he does have the power to match the heavier fighters (I don't think he quite does) there are a lot of different things to take into account in a different weight class.

I can hit a punch bag as hard as a lot of fighters who out weigh me by at least 10kg... I have the fire power to hang with them but on the purely physical side of boxing there's still more going on... Your ring craft and everything has to change it's much harder to move around the gym... have an effective jab and bump shoulders etc.

There can be a large gap in class but you still become more equal because of the weight difference when it comes to sparring these guys.

Power and Strength are two different things.

Manny would need a better boxing brain if he wanted to go much higher than 135 in my opinion.