Thjats right, forgot to mention it earlier. the head i saw was accompanied by a odd shaped rocker cover, wondering if anyone could shed some light... it has a slope through the middle long ways.
ill try to draw a cross section:
______
=> / |
=> / |

!!More like a 45 degree angle where the arrows are pointing
This is a front on cross section, facing the engine bay. The rocker cover lookds really good. would like nice well done up in a tidy engine bay

if memory serves me correct, it's probably off an F10, or a 310 (N10) front wheel drive.
also called a "cherry" some places.
the engine was mounted sideways and the slope to one side was to clear the air filter housing and other hoses. the airfilter housings in these models (at least here in usa were oval in shape with a larger air filter.
hope this helps.

I'm running an A-series N10 here in Aus and the rocker is exactly the same as the rear drive coupe. Dunno what you've got - could be import?

for what it's worth, i can only speak of what I know of USA model Nissan/Datsun products
based upon almost 8 years of working for a dealership.
I don't know for sure what was used in other areas of the world, sorry

you havent mistakenly confused the ashtray for the rocker cover have you? just kidding...
I think mine is like that too - is one edge on an angle? they are off the imported later model a15 if so...

Linc.