Thanks for the inputs guys -
I followed v4lu3s's suggestion that maybe the engine number had been shaved and re-stamped, so I went out and had a look at the block and ran a key through it to see if there was any inconsistency in the compound. It was solid. I ran it around the 'Z' to make sure it was possibly shaved out but upon close inspection, the metal surrounding the Z was extremely flush with the rest of the letters. The metal of the whole area around the engine number was consistently in the same 'age' or oxidization.
I'm still convinced that there is a number, perhaps it is a component that is only made for certain countries perhaps? I have updated the site - this time with videos.
VIDEO 1: This is a video starting from the engine bay, from which I then moved the camera and wedged it into the engine number area to finish on the number. Apologies if it is slightly dark on this one, it was early in the afternoon in the shade.
VIDEO 2: This is a video just after video 1 with my camera set to MACRO mode to be able to get a better zoom on the actual number. As you can see, the "Z" has a little silver dot towards the bottom - this is where I had ran a metal key through it to check the consistency as previously mentioned. The video then finishes with me taking the camera out of the gap to a blurry engine bay (since macro mode was activated) - I also adjusted the exposure to make sure it wasn't too dark when I moved the camera closer to the number.
The camera I used was a Canon IXUS V, with avi video encoding. Preset to high exposure and 640x480 resolution. I did everything I could with the camera's settings to make sure I get across that the photos supplied previously were no hoax.
So there you have it, I'm just as puzzled as everyone else is, but probably the most confused since it's actually sitting in my prelude at the moment after a recent engine conversion *sigh*.
Videos found here:
http://members.optushome.com.au/compsoc/h22z
I have taken the photos off - but if you need to have a look, I'll put them back up again.
Thanks!