These thermostat housings will fix your leak with a gasket seal design. This design works with a Mopar thermostat only. Late model Chrysler style thermostats suggested. Neck goes straight up, must use Mopar thermostat.
Chrome Water Neck Fits Oldsmobile 330 350 455 Olds Engines
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Mr Gasket 9713 Chrome Water Neck Fits 79-97 Ford 5.0L / 5.8L 302 / 351W V8
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SBC BBC Chevy 15deg CHROME WATER NECK THERMOSTAT HOUSING WITH TEMP PORT #9468