Fresh 302, block was decked, valve train noisy

As for the too long pushrod question, if the pushrods were too long your valves would just never close. You shouldn't have any valvetrain noise with too long of a pushrod as the problem with the scenario is that you would have no clearance anywhere. If the pushrod where too long then it would take up all the clearance that is built into the lifter, and it would basically jam the lifters internal piston into the bottom of the lifter. Since you now have no clearance anywhere the valves will basically never close. If all the pushrods were too long you would probably have no compression, the engine would not start.