Had the same problem with my upper radiator hose in my 66 c10 shortbed stepside. I went from the stock 18 1/2-inch 2 core "mickey mouse" radiator to a larger 25 1/2-inch 3 core box and ran into the same dilemma. Fortunately Pep Boys had a flex hose with different sized ends. Cost about 15 bucks. I also had a great sales person who went above and beyond to find this hose.
I know you've resolved your problem but just an FYI for future reference, one does exist for your needs.
-ftyler
