I agree because it is a stock small engine. MP just outfitted what is basically a OEM 5.9 Magnum with a carburetor intake, 750 carb & 1-3/4 headers to get what they did and label it as 300hp as not to disappoint anyone when it dyno’s more.
All stock V8 engines gain power with dual exhaust and header a wee bit more. The big deal of headers isn’t so big on the above but becomes a wider and wider gap as the power goes up.
Headers were always a great first step.