Im looking for opinions on this block I wasnt able to link this from ebay but it is Item 123557081350. Ive seen a lot of early 721 blocks and I have some with 63 cast dates . This one is intriguing to me because of the very early casting date and the fact that it has the 721 cast upside down on the sides of the block. I know the 721s were used for 283 and 327 applications, but Ive never seen any of the early ones (pre-63) with the upside 721 because to my knowledge the pre-63 casting became 283s for 64 production cars and the upside down 721 blocks were bored up to 4.00 " for 327 applications. This one has the upside down 721 and a casting date of Nov. 17 1961. He tells me the block started life as a 283 and is at .060 over . Before this, the earliest 721 block Id ever heard of had a 1962 casting date.