A 3 core will work fine on the 289. You can use a mustang radiator, just about anything will fit in your galaxie. I would check NAPA auto parts, they have a book with all dimensions and hose locations. I recently bought a 3 core for around $200. Most original 289's are 2 core, so even if you get a slightly narrower (mustang) radiator, as long as it's a 3 core it will work. My car will run 180 to 200 Degrees on a hot Norcal day (on the open road) in stopped or slow traffic it will run 240 - 250. The only way around running that temp is an aluminum radiator and an electric fan. A nice set up can run you $600 - $700.
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