Yes , as I understand it NICSON introduced the 15 bolt head in 53 and as we know chev. changed to 18 head bolts in 54. I've been told the molds were being changed to 18 bolts when chev. introduced the V-8 in the 55's and at that time the work on the 6 cyl. head stopped. I know there was some v-8 stuff was produced but they concerntrated on mostly marine stuff after that. I have been told there were only 36 heads cast-they were cast in lots of 12 and they only ran 3 castings.I notice the head in HOT ROD was iron so I don't know how many of each were cast. Due to srinkage wouldn't it be difficult to cast both in the sane patterns? The imfo. I got was from a 74 [10 years ago] year old man who told me he was the main machinist at NICSON and did most of the work on all of them. I have his mane here somewhere' Just ran across it a month ago. When
