[sixtiesmuscle]

The general belief is that:
1]Small block cars were used in early '67 model year, but, once the big blocks were available, those cars were preferred to be used for transplants.
2]The 396/375 engines that were pulled were easier to sell to the "hot rod" crowd than small blocks, plus the installations were much easier because they required less modification.
3]If a customer wanted a particular car, color, whatever, they would convert that car whether it was a big block or not. Inventory probably dictated much of what went on.