I have a 400 cid(6.6L 4bbl NA Turbo400) in my 1973 Grand Prix J with a block VIN code 25A127360, engine block casting number 481988, date code A215, engine block code YT, motor unit number 0234326. There is a 75 and 2 D<)N next to distributor pad. Most of this information seem to indicate this engine was original to a 1975 model but the block casting code refer to a 1974 model. Can someone decode and determine correct year and which model this engine was original to? Are there other codes or numbers on engine that will further identify the original year and model?