Ok, here's what you do:
1. Turn the engine over until you are approaching the #1 TDC. You can do this by turning it over and putting your thumb over the #1 spark plug hole, and you will feel the compression. When you feel this, stop.
2. Install your harmonic balancer (if you haven't done so already), and the timing tab should be in place also. Continue to rotate the engine until the timing mark on the balancer reaches 12 degrees (BTDC) on the timing tab. You should now be on 12 degrees BTDC on the #1 cylinder.
3. Take your distributor, and install the cap and rotor. Now, take a marker or whatever, and mark on the distributor BODY (not the cap) where the #1 plug terminal is on the cap. Take off the cap. You should now be able to determine where the #1 plug terminal is without the cap installed.
4. Install distributor, with rotor installed, but not the cap. You will probably have to turn the rotor counter-clockwise a bit for the rotor to reach the #1 terminal (the mark you just made), because the distributor gear is ground helically (curved). Try to keep the distributor body in the same position as it is in stock configuration.
5. If you find that the distributor wont seat fully, take a long, clean screwdriver and rotate the oil pump (through the distributor hole), and reinstall the distributor. You may have to rotate the pump several times for it to get seated fully. Some people just bump the engine over until it seats, but I like it to seat fully before I rotate the crank.
6. With the distributor seated fully, and the rotor is pointing in the general direction of the #1 mark that you made, rotate the distributor body until the rotor points exactly at the mark. Tighten down the distributor, and reinstall cap, wires, etc.
You should now be able to start the engine with 12 degrees of initial timing. 12 degrees will usually provide very quick starts, assuming the carburetor has fuel and you've primed it (squirted some gas down into the intake via the throttle).
Fire the baby up and make some noise.
1969 Base Camaro
Vortec 350, TH-400
All sheetmetal is NOS GM