Years ago at the Pellow auction they were selling A/B heads by the pallet load. I ended up buying one of the pallet loads because I noticed a 2-pc case head in the mix which I wanted. The rest of the heads got stacked in the back of the storage shed. I decided to look at them and see if I could answer your question. If by "fin" you mean that the casting around the guide is slightly smaller and comes to a fairly sharp line on the inlet side, the fin was only present in 2 of the 13 heads. I have one with the "fin" dated, I believe, the 12th week of 1955 which was not a split head and one with the "fin" dated the 43rd week of 1956 which was a split head. The rest which were dated, as best I could tell, from the 25th week of 1957 to the 8th month of 1960 did not have the fin and were not split. Some had no dates or the casting mark with the date was not legible. Most did not have a maker id although a couple were apparently cast by Kolbenschmidt and except for the 1960 head all had no part number although they did have casting marks of 101/x where x was either 4, 7 or 8 which may have reflected drawing changes or pattern identification or casting vendor or nothing. I suspect the fin you are talking about is probably date related and nothing else.
James Davies wrote:
True! Though I think the first 616/2 heads were different from the 616/1 heads. They had a a split down the middle, partially separating the head for each cylinder, though I think this was only for a short time in 1956.
And perhaps the 616/2 heads also had a fin in each intake port shrouding the valve guide? I know the 528 and 528/2 heads had this fin. Did the 616/1 heads have this fin?