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1970 was 370 gross rating 1287 made
1971 was 330 gross rating 1949 made
1972 was 255 net rating 1741 made
The difference was 1970 had 11.1 pistons and 71 and 72 had 9.1 pistons. 71 and 72 the engines are the same they just rated the HP differently to probably lower insurance rates. Net rating is with all accessories on the engine Gross rating is just the engine on the dyno. AC was only offered in late 72