BigD, you're not listening. There is no stock horsepower rating on this motor because it's not stock. It's an abortion that someone has cobbled together from different parts that were collecting dust under the shelf. From what you've said, you've already found the max rpm of this motor, 3,800.

Bite the bullet, pull this turd out and build yourself a 383 or 400 small block 2-bolt main that will have enough torque to haul this boat. Look at combinations 15 and 16 of these dyno-proven 383 builds and pay attention to the torque figures.

http://www.ryanscarpage.50megs.com/combos2.html

The compression ratios will also be "marina-gas friendly".