Again, thanks for the comments!
I don't think that engine size was any determining factor as to weather it was equipped with AIR or not. But rather it was a means of getting the engine to comply with HC standards for any particular model year. Also, California had its' own set of standards as set by CARB, which were more stringent than the federal standards set by the EPA. As such, you will find engines of the same displacement, over differant years and differant power levels that were or were not equipped with it.
The 1970 LT-1 certainly was, as was the LS-5 and LS-6 454's. However the standard 2BBL 350 was not, nor was the L-48 300 HP 350. But as standards became more stringent, by 1974 all 350's and 454's were equipped with AIR. 6-cylinder engines were not.
Cadillac engines were another example. All 1968/69 472's were equipped with AIR, but the federal 472/500 for 1970 was not. They used another technology called Transmission Controlled Spark (TCS) that year, however California engines did use AIR. From 1971-1974 all federal and California engines used AIR. With the advent of the catalytic convertor in 1975, only California engines again used AIR. This remained through 1979 with the 77-79 425. beginning in 1980, all cadillac engines were equipped with AIR, and that would last through the HT4100, and 4.5 V-8's until the 4.9 was released in 1991, which did not have AIR. Fuel injection technolgy had come to the point where it was unnecessary.
As a rule, so far as I have seen anyway, Chrysler used AIR only for the California market at least until the late '70's. Ditto for Ford.