As Breezy indicates my early 216 Canadian trucks had 1 1/4-inch thermostat housings and upper radiator hose connections and later 235 engines had 1 1/2-inch housings and upper radiator connections . The 1955 second series water pumps and lower radiator connections were 1 3/4-inch while the older models had 1 1/2-inch on the pump and radiator. Some vendors offer a lower hose with 1 1/2 inch on one end and 1/3/4 inch on the other to allow use of newer pumps with an older radiator.

1954 Chevy 1300 engine 235 (1959)
1955 (first series) Chevy 3100 engine 261 (1957)
1927 (other brand) Model T- engine 327 (1968)