The 500 Delta Head produced from 1957 and 1959 although some casting date codes are reported to run into the sixties.
Note the register around the combustion chambers to allow for the sleeves in the 500 alloy barrel. This head is very similar to the first T120 heads, this register is the difference.
Spigots for the single carb manifold still in place, later versions lost these.
E3663 seems to be a popular part number, there are several head designs that share this number.