Spark at coil and distributor but no spark after plugs installed and crank at key

To set the idle-timing and low-rpm timing you don't need to be accurate.
It will start or try to with the timing anywhere from between 5* retarded to about 25 or even 30* Before.
And with the right amount of throttle opening will also run there.
And then you can even set the idle-timing by ear.
What Ima saying is that with a factory-type distributor, it is almost impossible to give the engine the idle-timing that it wants anyway, and still be able to drive the vehicle......... so accuracy at idle in this case, is just not a big deal. I certainly would not go out and procure a piston stop just for this endeavor.
Having said that you may need it for setting the Power-Timing.