On the surface one could read you number as.
55 = year
F = Flint
10 = Month
17 = Day
N = Engine 6000 Series HD (261)
But as TC said that's not the format used in 1955 1st or second series.
Then throw in the date code of Jan 27, 6 ...is this 1956 or 1966???
IF your block is a replacement the format is correct for 1966 (F1017N) except for the 55 prefix. Could this be a 1966 cast replacement 1955 model block and Chevrolet added the 55 to identify the model year and N to identify it as a 261?
Thinking out loud here...
Mike B
