What Datsun Roadster is this?

It's either a Datsun 1600 or Datsun 2000, which there should be an emblem on the fenders to tell you which one. I don't believe the grille is original. They were made from 1965-1970 and were also known as model SPL311 (if it's left hand drive; if not, drop the "L"), Datsun Fairlady and/or Datsun Sports. The 1600 and 2000 designations referred to the engine displacement in cc's.

That looks like a 1969 due to the teardrop front side marker lights. They were on US models for just that one year. Although some teardrop side marker cars were registered as a 1970 due to a lot of the Datsun dealerships registering a new car the year in which it was sold and not the year the model was released. It is a left hand drive as it has the US DOT required and "correct for the year" drivers side mirror.
2000 or 1600 model? Without opening the hood, if it has a 4 speed manual trans, it is most likely a 1600. The 2000 has a 5 speed manual transmission, although, a modified 1600 stroker engine will usually be paired up with the 2000 5 speed.
Only way to know is to open that hood. Maybe you get lucky and it's a 2000 with the rare $$$$ Solex manifold with PHH 44s on it.