1991 Chevy Blazer seting timing

2.8 and 3.1 liter @ 10deg and 4.3 at 0deg

If its a 4.3 dont forget to unplug the timing advance, located under the carpet on the passenger floor- just beneath the heater core. And it will be 0 degrees TDC. If your not sure where TDC is, look on your harmonic balancer there is a line on it, or you can pull out the #1 cyl sparkplug and hold your finger on the hole while someone bars the engine over. When the pressure pushes your finger off, thats TDC.