1997 Chevy Truck how to set #1 piston tdc to to replace dis

There is no timing mark plate on engine block by harmonic balancer to set my #1 on tdc. I have taken out #1 spark plug and stuck my finger in the #1 spark plug hole and cranked the engine untill compression pushed it out but I do not have a way to find a mark to relate to set back or forward on the harmonic balancer. My friend took this truck to a shop and they told him that this engine did not have timing mark plate. They advised him that those engines were manufactured like that. If this is true, how do you find true tdc to set my rotor to point to my #1 position on my distributor cap. The shop also said that the computer automatically sets the timing in the distributor. I would really appreciate your help. Thanks in advance.