While you can never go too far wrong with too much drivetrain strength, it would seem to me that a NV3500 gearbox could live happily behind an LT1 or other V-8. The NV3500 is half the weight of the NV4500, less expensive, and easier to find. New Venture's own spec sheet says the NV3500 is good for 300 ft-lb of torque in a 7200 pound vehicle.
That said, I'm putting a NV3550 with my 4.3 Vortec, so I'm a little over spec'd too. But, I'm not sure I'd ditch this lighter NV if I switched to V-8...