How do you find TDC on a 350 Chevy?
First: NEVER insert a screwdriver into the spark plug hole to find TDC. You can nick or scratch the top of the piston head, which will cause hot spots which in time will crack the piston head which in time will mean you will be paying for a major engine rebuild! Instead, use a plastic (not wire, not wood) coat-hanger cut along it's longest length. Second: You need to know more than just where TDC is for most applications. What most people really need to know is where is TDC on the COMPRESSION stroke. (The stroke where the spark plug fires, rather then the exhaust stroke where the piston pushes the waste gasses out of the combustion chamber at TDC). You do this by putting your thumb against the hole where spark plug # 1 goes. Then rotate the engine by hand (ALWAYS clockwise if you are standing in front of the vehicle, facing it) and wait until you feel a large puff of air escaping. THAT is TDC on the compression stroke. Pull off your Distributor Cap and look at where the rotor is pointing. It should be pointing to Cylinder #1. If not, you either mistook the small puff of air that happens on the exhaust stroke for the big puff of air that happens on compression, OR, your distributor is not seated right in the engine.
BTW: Cylinder #1 on a Chevy 350 V8 is on the front left (meaning driver's side of the engine closest to the front of the vehicle.)