E-boss

i have a mustang 5.0 with Cleveland 2v heads on it everything bolted on it the intake that its suppose to have forged pistons (domed) built for the motor with the heads a holly 650 double pumper high performance cam push rods high flow water pump and oil pump. i have spark it will fire up but will not run for long only about 20 seconds.??? i dont know what it could be?

You say you have spark but how about fuel? Have you checked the fuel pressure? Check your fuel filter to see if it is plugged.