I think they just add marks to a GM balancer, and the zero should be much deeper and easy to see? If that is the case, you can either use a timing light that allows you to dial the advance into it, or there is a simple way to measure and determine a 36 degree mark that you could use for total timing. If you measure the circumference of the balancer, either with a flexible tape measure, or even a piece of string or wire, 1/10 of the distance will be 36 degrees.