First time down the track

Simulators are not even close a lot of times, sort of in the neighborhood some of the time, and dead on rarely. Weight and MPH. Gearing, traction, doesn't matter. Track results do not lie - so you are down on power. Question becomes "why"?
If we go on head flow at a little shy of max lift - in the mid 400 range at the valve, you have to be getting 225cfm to get 450hp. The stock LA heads will flow close to that. So I'd say there's a mechanical problem (valve job, assembly, cam timing, etc) or a problem with the porting. If I had to guess. This assumes the timing curve, ignition, and carb are all set properly. Do a leak down. DO a compression test. See what the numbers tell you.