When looking at Datsun racing history, it seems that the Datsun convertible sports cars in the USA in the early 60's were the first track racers and winners after the war: http://www.nissan-motorsports.com/ENN/NISSAN/HISTORY/MOTORSPORTS/index.html
The USA convertible sports cars were also the first racing cars to be sponsored by Nissan.
Datsun seems to have done a bit of track racing in the 30's and 40's but stopped.
Datsun NL-75 1936
Apart from Nissan's well known 1958 headfirst jump into rallying that was spurred by Mr. K. ....
1958 Australia Mobil Gas Trial
Nissan did little in Japan until after a non-sponsored privateer, Genichiro Tahara, won solely on his own effort at the 1st Japan Grand Prix Race, Suzuka Circuit, spring 1963. It seems this kick started Nissan into its racing activities in Japan.
Genichiro Tahara Winning at Suzuka 1963.
SP310_first_race_Japan_1963.mp4
In the USA things were different; Datsun's were track racing for the previous 3 years (since 1960). Mr K was in the USA and things were moving much faster than in Japan (both cars and Nissan-sponsored racing involvement).
The fact that no convertible sports cars were sold in Japan for two years, the fact that Mr. K was the motive force at Nissan for racing, the fact he was now situated in the USA, and the fact he requisitioned a sports car for the USA market, affirms the 240z sport car was designed and built for the USA sports car market.
Jean Le Plant and Benny Ackermann raced an SPL-212 in 1960 & 1962 then switched to the SPL-310 in 1962
Norah Taylor raced an SPL212 in 1961
Modernized "Datsun 1200" SPL-212 Commemorating Nissan's first Sponsored Racer: Jean Plant's 1960 LHD SPL-212 #129 Datsun 1200. It Raced from 1960 to 1963 in the USA.