400 "super block"
It ends in 230, and has different typeface than later blocks. 400 blocks with casting dates from 4/4/1971 to 10/10/1971 are the thicker webbing. After that period it can still be a 230 casting but it won't be the thicker web. From what I'm told any 400 block is a good choice, as long as it passes mag and sonic test...if you're doing something max effort just buy an aftermarket block.
Here's mine I bought last fall, casting date 9/3/1971:
http://i1286.photobucket.com/albums/a611/MPR_Chassis/T2eC16ZzEE9s3YbBSCitlNYw60_57_zps6e5d547c.jpg
It ends in 230, and has different typeface than later blocks. 400 blocks with casting dates from 4/4/1971 to 10/10/1971 are the thicker webbing. After that period it can still be a 230 casting but it won't be the thicker web. From what I'm told any 400 block is a good choice, as long as it passes mag and sonic test...if you're doing something max effort just buy an aftermarket block.
Here's mine I bought last fall, casting date 9/3/1971:
http://i1286.photobucket.com/albums/a611/MPR_Chassis/T2eC16ZzEE9s3YbBSCitlNYw60_57_zps6e5d547c.jpg
