Measure your nipple diameter on the radiator and the nipple diameter on the water pump.The local auto parts store will have it in a flex hose.I had the same problem when I put my 54 261 in my 51 Chevy truck.
I believe I went with a 20" long gates #25530 flex hose.
flex hose 25530 I tried the gates #20230 and took it back,must not have fit.
Tim