check this out on that car -
http://en.wikipedia.org/wiki/Datsun_Sports

you say it's a 1968 1600 Datsun  Roadster ...........

last of the series was produced March 67 to April 1970,
with 2 liter engine and 5 speed trans.

some interesting reading there , for example -
"The first-year cars are most-desirable today as there were just 1,000 to
2,000 produced and are unencumbered with the emissions and safety changes
introduced in 1968. The new SOHC engine produced 135 PS (99 kW; 133 hp). An
optional Competition package included dual Mikuni/Solex carburetors and a
special camshaft for 150 PS (110 kW; 148 hp)."

I worked on 'too many' of those 2.0 OHC Datsun engines.
been there, done that, burnt out on 'em. Tough engine though.
It's nearly impossible for the bottom end of a Datsun ( or Nissan ) engine
to wear out or fail.

Scott
turbovans.com