The Mustangs and Barrcuda's were mid year. The discussion I was having with the guy was the release of the 273. It was not available in 1963 but was put into production in 64 and not 64 1/2. Yes, blocks were cast in 63 because the 64 production year started in August of 63. He swore that 273's were a mid year production change in 64. Nope.