I think it's 226 cu. in. 4"bore 4 1_2 stroke. The design started as a 4"x 4" in the WC tractor in the mid 1930's. Changed thru the years and increased stroke to 4 1_2, increased compression, etc.
I own a later one. An E3 has a 226 cu. in. four cyl.engine. AC dealer told me this was the D17 engine. Built from '67-'69. Were predecessors to the K. They carried the chev. 292IJ six cyl. engine. I think not though. This is the F engine and the K was six cyl. but less cu. in. Hope this helps.