Re: 283 pistons
 

I ran a 721 block for years with arp bolts and stock caps ,broke it so many times that the caps no longer had that pinch on them but it was fast. Turned it 9200 all day long. One thing you would what to look for is where the cam tunnel is at, I have seen pretty bad ones over the years. That core shift would somewhat tell how thick the clys would be but are a over 100ths + thicker than a stock 283 block . The 721s also were suppose to have a better main webbing in the block itself and a higher nickel content, that info I got from a old chevy performance book. I have a fresh 721 waiting for when I get my car done 4 bolt caps filled 50 mm roller cam bearings and still 30 lbs lighter than a bowtie block. I am always looking for them and they are really hard to find now days Tom