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Try this:
http://www.geocities.com/MotorCity/D...00/cmspec.html
the factory did make some changes on casting# 3904366, part# 39043362 camshaft over the #143 cam. Valve events and duration are a little bigger.
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If the specs are different on the measurement, I would assume that it is the variance in production tolerances.
Jim
PS.....Colvin has a blue print in his "Chevrolet by Numbers 70-75" in the camshaft chapter on the 3904366 casting.