To find precise TDC is easy. Make yourself a piston stop tool out of an old gutted sparkplug.
Remove sparkplugs.
With piston down the bore a bit, install piston stop in motor and carefully rotate until the end of tool contacts piston. Make a mark on the timing pulley in relation to the TDC mark on the timing cover.
Rotate motor backwards carefully until tool contacts piston again. Make another mark on pulley.
Halfway between the two marks is TDC, file new mark and paint white so it stands out with a timing light.