Those dyno results are right-on for your combo....Those are Rear wheel numbers, so 280 is not bad. My old hyd cam 440 combo made 420 hp at the wheels and ran 11.60's...and that was with headers, single plane intake, 800 DP holley and aluminum RPM heads and 10.2:1 compression.

Combo is everything....find out what cam you have and compression ratio.