No 1st gen barracuda's came with a 318, which would have been the Poly at that time. The 273 was the first of the new "light" casting Chrysler engines during the 1964 model year, which are the LA engine. The LA318 was introduced for the 1967 model year, but didn't replace the 273 until the following model year, 1968
1966=VIN for the 273 2bbl(31), 273 commando (32)
