Another way to think about this is that the cam and distributor are a 1:2 underdrive to the crankshaft....so the crankshaft makes 2 revolutions and passes the TDC marker twice as the distributor rotor makes 1 revolution. You have to pick the TDC event that happens on the compression stroke...the rocker arms for the #1 cylinder will be "quiet" on both sides of this TDC, on the other, "incorrect TDC" the intake and exhaust valves/rocker arms will be in motion as the combustion cycle is shifting from exhausting to intake-ing.
When you have the GM ignition module (small cap distributor, round-ish cap) it needs to be put in "base timing mode" which inhibits the module's electronics from doing any spark advance. When you look at this distributor there's a solid shaft to the rotor, there's no vacuum advance, there's no mechanical advance. The entire advance curve for all speeds and loads and starting is bult into that module. (there is a provision for retard modification if knock sensing is present). The jumper harness mentioned above puts the ignition module into base timing mode. I extended the wire with the alligator clip on mine so I could reach the battery in the next compartment over....nothing more sophisticated than a couple of butt splices and a piece of stranded wire.
It is theoretically possible if one randomly chooses the TDC marker on the crank wthout checking, the distributor can be 180 degrees off. A short term fix is to reposition the spark plug wires based on the same new #1 on the opposite side. That should be good enough to get running but there are usually some bad compromises in the spark plug routing that result. So if you find yourself in that situation I urge you, once running, to stop and hand--crank the engine exactly 1 more revolution and reset the spark plug #1 to original. Your spark plug wires will thank you for this.
