Ah......another run-on-one-engine aficionado like me. Be prepared to be flamed by the purists!
Seriously, I also have a Hatteras that used to be powered by Detroits, but they were 871's. I don't have the hp / torque metrics that you're seeking for 453s in a 48 LRC, and I don't know their rated rpm, but it wouldn't surprise me that you could nearly get to hull speed by having one side to the pins. I'm sure the Hatt LRC drivers will chime in. A related question is whether your gears can be free wheeled or if you have to lock the shaft to run on one. Most Twin Disc gears can be freewheeled. Allisons, for one, can't.