#1 post on distributor

It is easy to remember which cylinder is #1 in almost any engine. It is the cylinder at the front of the engine. In a V-8, the cylinders are not exactly across from each other. Only one connects to the crankshaft first. Look at the block closely. In a transverse engine, the "front" of the engine is where the pulleys are. The transmission bolts to the rear. There are a few V engines where the connecting rods share a single rod bearing and are thus exactly opposite each other. I once designed for a large stationary piston engine like that, and I think some V-twin motorcycles are like that.

Re your original question, many Mopar V-8 distributor caps have a "1" with rotation arrow. Actually two 1's with two arrows for small-block & big-block, resp., so you must know your rotor rotation to know which "1" applies to your engine. Of course, as others mention, the marked post will only be #1 if your distributor drive gear was inserted with the slot pointing correctly (at #1 intake bolt when TDC).