408 Stroker

Most likely it's the cam that is holding it back. Like mentioned, something in the 250* range and 550 lift is what it needs. Looks at some of the recent builds that approach 500hp, not many, if any have a cam with duration/lift that short.

If the heads were ported and they did a bad job on it, that could hurt as well. Those heads with nothing but a 2.02 installed and blending the throat cut are capable of 520hp with the proper compliment of parts.

The headers might cost 6-8hp compared to a tti or supercomp/hussler. Not a good gain for the dollars you'll spend to go another direction. IMO, better money spent elsewhere.

Don't get sucked in by dyno numbers. I know some guys that "know" big numbers sell engines. Those same mills don't seem to run like a lower HP engine MPH at the track. It's pretty commonplace in the world today, like "my dad can beat up yours" or "my johnson is bigger than yours", etc. Proof is when they run the MPH at the track and I've seen PLENTY of disappointed people over the years. Just watch pass time and the 700hp cars that run mid-high 120 mph ranges at 3200-3400 pounds... ummmm yeah right 700+ hp LMAO, NOT A CHANCE.