If you have the timing marks, line up the "0" line with the timing pointer on the balancer. But since that can be a problem with swapped engines that may not have all the right parts put together (wrong balancer for timing cover, pointer deleted to fit lower rad hose, whatever).
Without actually pulling the engine partially apart, true TDC is almost impossible to find. But you can get close. Pull the spark plugs, spin the engine over. With a finger over #1, you will feel air pushing your finger off the hole. You are coming up on TDC compression stroke. Go too far and you will feel your finger start getting sucked into the plug hole. That is ATDC on the power stroke. Between those it TDC.
Plan B, remove the bolt holding the balancer to the engine. Don't remove the balancer. Look for the keyway. Keyway straight up is TDC. Just don't know if for compression or exhaust without looking at valves or the finger trick.
Plan C, unclip the cap off the rotor, line up the pointer with the #1 marked on the cap. Fine tune with lining up the reluctor ring, edge of the hall effect wheel or when the points open. But this is the least reliable way as you also take in timing chain stretch, distributor setting, alignment of timing devise, and any other issues thaqt may creep up. But depending on what you are trying to do depends on how much wiggle room you can live with.