It's the 230 and 283 pistons that are identical, same part #, the Chevy part numbers too.
see:
http://www.beckracing.com/slvpg25.htm - 230
http://www.beckracing.com/slvpg27.htm - 283
Using 307 pistons in a 250 is supposed to yield 9:1 compression.
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Pete Geurds
64 Malibu SS
64 Chevelle 2dr wagon
64 Malibu 4 dr sedan
