Ran across this site last night:

Online Manuals

Of particular interest was his copy of Datsun Technical Bulletins from 1969-1972. It answers questions about when and where the head gaskets were changed, and the corresponding head bolt change. As well as a good description of the dual point distributor setup.

One bulletin was of particular interest regarding oil leakage at the head gasket. It was for a smaller engine, but I've had a recurring problem with an oil leak to the outside between the #3 and #4 cylinders even after changing the head gasket. The bulletin shows an oring being inserted inside the gasket opening for the oil galley feeding the head. Could be a workable solution for my problem.

Lots of good information contained in this manual.

I finally got around to reading the TechBulletins 69-72 and extracted those numbers applicable to our Z's.

Of interest, I found the tech bulletin that described the phosphor bronze washer added to the rear stub axle assemblies.

Another bulletins states that the first production Z's with electric rear window defroster was serial number HLS30-01456.

Here is my list sorted by Bulletin Number

zTechB6972.xls

Please also post the xls in this thread: http://www.classiczcars.com/forums/misc-s30/48293-technical-service-bulletin-thread-tsb-click-download.html