Published 2009
Valve Cover Development
Single carb 1500s - chromed valve cover with a chromed D shaped breather - unvented cover.
Dual carb 1500s - finned aluminum valve cover with no spot for the vent tube - round chromed open breather.
Late dual carb 1500s and early block vented 1600s - finned aluminum valve cover with spot for the later breather tube cast but undrilled - either a round vented breather cap or a tower with a fitting to vent to the air cleaner.
Later 1600s - finned aluminum valve cover with breather tube and unvented round oil cap. These also had the back end of the cover modified to be "clipped" a bit to clear better when removing the engine from the engine bay.
The Silvia had the finned aluminum valve cover with Nissan on it rather than Datsun. I have not noted variations in it, but there likely were a few...