The ignition system causes a spark inside each of the engine cylinders. If the spark happens at just the right time, the gasoline – air mixture in the cylinder 
explodes causing the pistons to move and the crankshaft to turn. The main parts are the spark plugs, spark plug wires, and the distributor, which as the name implies, distributes the electrical energy among the cylinders. The distributor and spark plug wires are in the picture on the right. The distributor has thick wires attached at its top, and these carry electricity to the spark plugs.
Inside the distributor is a pointer, or rotor, which spins along with the engine. When the rotor is aligned with a spark plug wire, 
the distributor sends high voltage to the spark plug, which in turn ignites the gasoline-air mixture. The position of the rotor relative to the spark plug wires can be adjusted by turning the distributor itself. This adjustment is critical to a well-running engine. It requires a two-step process.
First, the engine crankshaft is turned to a specific point. Modern cars use electronic sensors to know the crankshaft’s rotational position. Older cars, Sunbeam’s included, are more primitive. The mechanic rotates the crankshaft with a wrench or socket until it is aligned with a specific fixed point on the engine. To the right, the pulley is attached to the crankshaft and is marked with horizontal lines that correspond to the position of cylinder number one. The white dot to the left of the pulley is a fixed alignment point on the engine. For my Sunbeam, the idea is to line up this mark with the fifth horizontal line on the pulley. This position should correspond to the distributor sending 
electricity to the number one spark plug. Note that the dot and lines can be difficult to see. Workshop manuals say to use typewriter whiteout to make them visible. A sign of the times.
In step two, the mechanic rotates the distributor until the sparking mechanism is about to fire and the pointer, or rotor, is is lined up with the number one spark plug wire. To the right is the distributor with its cap and wires removed to reveal the rotor and inner workings. Unfortunately, the brass pointer is angled down, when it should be up for cylinder one to fire. The engine could not run with the distributor set in this configuration. Had it been exactly 180 degrees off, I could have simply switched the spark plug wires. I was not that lucky. 
It turns out that the distributor is driven by the engine’s oil pump and that the oil pump and distributor can fit together only in one orientation. The picture on the left above shows the oil pump shaft and its two slots. If you look carefully, you can see that the slots are slightly off center so that the semicircle on the right is slightly larger than on the left. The distributor has corresponding wedges that fit into these slots. In consequence, I could not simply lift the distributor up and rotate its shaft 180 degrees. I could have used the distributor that came with the new engine, but my old one was in much better condition. 
What to do?
My only option was to rotate the oil pump shaft 180 degrees and start again with the distributor and ignition timing. This is not a hard job since the oil pump is held in by only two bolts. But I needed to remove the oil pan for access. Fortunately, the oil pan can be removed with the the engine in place. To the right is the underside of the engine exposed. The camera is looking up from the floor, and the oil pump is at the back of the picture. The donut-shaped part filters oil as it is pulled into the pump.
It worked. According to the workshop manual, the slots in the shaft should be at 48 degrees relative to the distributor mount bolt holes. Since the protractor I found in a drawer was too large for the space in the engine compartment, I made a template from cardboard with lines drawn at 48 degrees. You can see in the picture below on the left that the slot(s) are just properly aligned. The slots are close to diagonal line on the template and the larger semi circle is now on the left. The distributor rotor points upward.
Will it run?
Sunbeam 