Where do i set the ignition timing for my 1991 chevy 4.3L

most of those are set at zero and thenthe computer did the advanceing as needed while driving

At the front bottom of thr engine you have your harmonic balancer. This has a pretty noticeable groove in it (there's actually 2 of them). On the block in the the same area there's a protruding mark that you line that groove up with. The other groove will be at the 1 o'clock or two o'clock position. Once you have that lined up, the metal strip on the distributor rotor should be pointing at a small #6 on the distributor housing when the cap is off. If it's off just a bit, you have to go under the vehicle again and rotate the harmonic balancer one full time and line the marks up again and you will be in timing.