4.3 is a 262. The slight difference in air volume won't be critical, as the O2 sensor will fine-tune the mixture once the computer goes into closed loop operation. You'll get a slight over-rich condition on full throttle acceleration, but that's also a good thing. Most of the race engines we checked on the dyno had a wide-open mixture of slightly under a 12:1 air/fuel ratio instead of the 14.7:1 stoichiometric ratio that the O2 sensor is looking for all the time.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
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