55 cylinder heads
like to learn what date the last 523 heads were produced and the last vin. # that these heads can be verified using on the 55. owning a late september car the 306 heads are the ones that seem to belong on the car . i know the 306 have castings in august . the judging manual only list the 523 heads and i would think with cars being assembled into december it would be unlikely that the 523 would still be available. to make it easy for myself and others, at what vin. # would the 306 heads be acceptable on a 55.