The 260Z has a nominal 260 cc displacement I-6 that is carburated like the 240. Emission control requirements had come into effect and the structure of the car had been beefed up in a few areas so Nissan started making the engine a bit bigger to offset the negatives of additional pollution control equipment and a slightly heavier car.
It was sort of a stop-gap measure until they could get the fuel injected 280 motor out the next year.
Phantom , somebody asked about this one a week ago and I will restate for the record, some of the early 280Z 's in the NA application came through with 260 carbs on them. I have seen three so far with them on, one was running and two were not. The production dates were on the 12-74 and 1-75 280Z's. Again, I will restate, if anybody would like to see pictures of these cars for publication or just a Zcar history, the cars in the yard that I saw them in are still there and I will get you pictures of the carb system and the production dates from the identoplate on the doorjamb.