Dutch,
Sorry if I confused you, I was pointing out the markings as viewed.
I have corrected the post to confuse everyone else!
Julian,
The 1953/5 RR & SS both had the alloy head with the detachable manifold.
The RR used a TT carby and the SS had a 276 in 1954 and a Monobloc in 1955.
Maybe the "special" Daytona heads were only standard heads tricked up for racing.
The heads I have with the date castings are just plain old standard heads of the day, nothing unusual about them. I have seen a few of them, the SS being far more common than the RR here in Australia.
The RR177 head is different as it has no date and enlarged ports.
I bought it at a swap meet some years ago as my 1954 head needs a lot of work.
It is possibly an American import to this country as there has been a lot Aussie entrepreneurs scrounging about the U.S for a lot of years.
The actual part number of the head is 67-1105 for the RR and 67-1101 for the SS.
The SS valves,collars, bottom cup and colletts are the same as the standard engines whereas the RR has the increased diameter collars and cups with colletts to match the groove in the valves.
When you compared the heads for flow, which head did you test - 67-1126, 67-1549 or 67-1571?
Was the 67-1106 head stock standard with small ports and the single carb manifold fitted?
Attached are the RR parts pages from 1955.
Trev.