I have heard that there are two different ignition locks for the 240Z, one for the series 1 and another for '71-'73. Can anyone confirm or deny this and if this is true can someone explain the difference?

Very early cars had keys that were cut on one side only.

Here's a picture of the original 1970 Key for my car.

E:\Documents and Settings\Charles I. Vigdor\240ZKEY.jpg

The ignition locks of the series one cars were manufactured by two different suppliers and indeed have the single cut keys. The lock itself has the electrical auxillary from a plastic lobe on the side of the lock body.

There are two different length keys for the early ignitions as they were made by different manufacturers. This is kats' picture showing the two lengths (right), the typical door / hatch key (of which there are two different types) and the later double sided ignition key (left). The double sided ignition shown here is the early type. Later double sided keys have a more rectangular head.

My experience is that the single sided long key came along the same time as the suppliment instructions - early 1970 - and I see short keys on all the early cars.

Both single sided ignition key types are chromed steel with the offset lobe head and say NISSAN on one side. The long key has the manufacturer named stamped below the NISSAN. The short key is blank. Both have the dot pattern stampings on both sides. The two different types of door / hatch keys are bronze and identified by a model number stamp at a space along the bottom of the head. Both are enameled gloss black. The difference is in the cut of the grove on one side. Take a look at how close the groove on my keys is cut to the edge of the stem.

Now check out how the groove on this eBay key is cut down the center of the stem.