I know of two cars that APPEAR to have come with them, both were very late SPD cars. I've seen 4969/70/71 carbs with assembly dates as early as October of 1970 (date stamped K0) but have never seen an early built car wearing a set.
I think they had some sort of supply issue around that time which left them short on the 4969/70/71 carbs which led to the modified 70's being used on the majority of the 71 Hemi cars. Another possibility could have been that they had an abundance of 1970 inventory that needed to be used up and they had enough of them to use on the majority of the 71 production line cars.
Bottom line? MOST 1971 cars came with modified 4742/5/6 versions, which had either M9 or ML9 date codes (the "M" was stamped ahead of the L indicating it had been "Modified"). Interestingly, a 1970 carb dated M9 (December of 1969) was not stamped with a second "M" if used on a 71 car.
