The "old" way of doing it was to remove all the spark plugs (to make it easier to turn engine over.)
Then turn motor over while holding a finger/thumb over the #1 plug hole so you can feel the compressed air pushing out of the cylinder.
When the air stops, use a long thin screwdriver or a piece of wire (etc.) and use it to touch the top of the piston.
Turn / Rock the crankshaft forward and back until the piston no longer rises /falls. That's TDC.

You can use timing tape to replace the missing markings. Measure the diameter and call Summit for the right part number.


HTHs..