At 9000 feet, there isn't enough air getting into the engine to make getting exhaust out much of a problem.
That engine is BEGGING for forced induction/power adder. Any form of supercharger or nitrous is going to be a huge help.
At the point where you have the intake system appropriately pressurized, all the other stuff will make a difference--exhaust, cam, etc.
Gearing, scrapping the silly tires, or greater displacement are about the only things that would help without forced induction.
That engine is BEGGING for forced induction/power adder. Any form of supercharger or nitrous is going to be a huge help.
At the point where you have the intake system appropriately pressurized, all the other stuff will make a difference--exhaust, cam, etc.
Gearing, scrapping the silly tires, or greater displacement are about the only things that would help without forced induction.