Knock the 311 L89's off, because they are a subset of the L78's, ie you had to order an L78 to add the L89 heads. The L48 was included as the "base" SS option package, so 22349 of those Z27 were base SS's. Removing the 311 L89s leaves a total of 35998 SS engines, to go into 34932 "SS's", or a difference of 1066 extra engines, or a typo in one or more of the totals.