I have a used set of SRP big block chevy pistons, part number 212140. I grabbed one out of the bunch and it measured 4.493" so they do have some wear, but you can have your block bored and honed to match. SRP's description is: Bore Size: 4.500 Oversize: 0.030 Dome Volume: 17cc Weight: 680 Pin height 1.645" .990" Pin 508 cu. in. with a 4" stroke. Check their site for all the specifics. Price plus shipping. These are almost $600 new.
The Jalopy Journal
