How do you do this if you don't have the timing scale on the harmonic balancer?
Clean the balancer off.
If it STILL doesn't have the scale (mine showed up after I got a layer of rust off of it ... I used some citrolene cleaner and cranked it with the ignition off, I just LOVE my remote starter switch!), then there's always units like the Mr. Gasket tape I have on my 5.0HO (strictly because I had problems reading the scale, not because it didn't HAVE the scale ... )
Or upgrade to something like the BHJ balancer, which is clearly marked.