Think about which engine came in the first Datsun 510...it wasn't a U-series engine.
The first 510 was announced August 1967, with L13 engine. But the first L-series -- the L20 -- debuted...whoa!
1965The engine in the Austins that Nissan built didn't use the Nissan A-series engine, it was an Austin design (see Cusumano's book). After the Austin-Nissan era, the Nissan E-series engine came out, then the J-series, and after that, in 1966, the first Nissan A-series engine -- the A10 -- debuted. If you look closely you'll see it is not the same engine as the BMC A-series engine. There are many differences.