A straight up 5.7 truck Vortec has 255 HP and 365 torque with rollers and the heads you have and fuel injection. GM sellls the Ram Jet crate engine which is pretty much a Vortec and calls that 345 HP and 396 torque. Your L65 would have had 165 net HP 280 torque to be comparable with above figures. I'd say the mods on the engine are about 50 HP so that's around 225 net HP and 350 torque. So your 300 gross HP is in the ball park. A straight up Vortec would be 365 Gross HP.
