I just recently went through a similar situation w/a 79 250 in a 49 GMC. Due to previous hillbilly engr'ing I had to change the thermostat housing to the smaller 235 hose outlet which was smaller than the radiator's opening. I now needed a hose with 2 different sized hose openings. Armed with measurements, 10 minutes at a local FLAPS produced a flex hose that worked perfectly. You may have to go that same route.
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