You need to find true TDC on the compression stroke on your #1 cylinder. I would get a piston stopper that screws into the spark plug hole to be accurate. First find the compression stroke by turning over the engine until compression blows out the #1 hole and then back the engine up. I would also unhook the battery at this point. Install the stopper and slowly bring the piston up to it. Mark where the balancer is in relation to the block, usually with a marker. Turn the engine back about 360 degrees until the piston touches the stopper again. Mark where the balancer stops onto the block. Half way between the marks on the block will be true TDC. Remove the stopper and turn the engine back towards the compression stroke until the mark on the balancer lines up with the center mark on the block. This is where you drop in your distributor. You can also make a permanent mark on your flywheel too, to time the engine with a light after it runs.
Good luck,
Scott
