[MySons68C20]

Piston stop in #1 cylinder. Rotate engine both ways making sure you are on the firing stroke which you can establish by looking at the rotor position on #1 cylinder/dist cap firing. Just have to be sure you are on the firing stroke not 180 deg off. Split the difference between the 2 and that'll be tdc for #1. A timing tape is necessary unless your dampener already has marks on it.
There is a way to do it with a timing light but I've never done it that way. You will need to figure out a pointer bolted to the block somewhere to mark tdc on your timing tape once you have that established.
Hope this helps!