without taking off the head and placing a dial indicator on it with a degree wheel... ..this is the only way to get close other than what Bill said above.
continue as you did by taking off valve cover and getting both valves closed...check your piston in #1 spark plug hole and make sure the piston is up..its possible to have both valves closed and the piston NOT be at the top...this is called the OVER LAP....
Once you verify this and the harmonic balancer is on "o" degrees drop in the distributer with the rotor cap off. make sure the rotor button clip is pointed toward the #1 piston......lock down your cap ...then contiue to roll your harmonic balancer around to what ever degree you want the final timing mark set on ..examle: 36 degrees.
if your harmonic balancer was installed properly at "TDC"..This process will be dead on target and fire up No problems...
note: if this is a high performance motor there will be some issues on installing the cam on the marks straight up and down..normal low performance street motors this is a ok method..
Good luck.
Brian
__________________
Bjuice..
"I'M YOUR HUCKLEBERRY ! "