im 100% sure its a 406 i helped my buddy run the numbers when we first got it. i have since forgotten what they are. we ran the numbers because when we bought the car the guy we got it from thought it was an R code 67 fairlane. i ran the numbers on the block and heads with my buddy and it ended up being a 406. so im sure im getting what im paying for. the only reason im getting it at this price is bc im a very close friend and they are building a 427 for the car and have no use for the 406. i just figured if anything the carbs and intake are worth it