just bought a 72 240z and it has a newer (40k) datsun engine in it. the guy i bought it from swears its a from a 280z but its carburated not fuel injected and i thought that was the big change between the 260's and 280's. Do i have a 260 engine? Or some non-us version of the 280? how can i tell?

 

The block tag just below the cylinder head on the passenger side.

 

All L-series look very much alike, especially when dressed with the same induction, as in the 240 carbs and intake on an L28 would look just like an L24.

FWIW, my car came to me with an L28, and the '73 intake and carbs.

As mentioned the little flat at the rear of the engine, just below the cylinder head on the right side will have the engine designation and the build number.