5/8" heater hose and can only find 1/2" fitting

duster360 said

After looking up some pictures of Darts with these intakes I have come to the conclusion that I will either have to run the hose over to the drivers side, drill and tap the passenger side fitting to a larger size or get a '70 and up heater core ( if it will fit ) to put in my '67 Dart.

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Why not use a 3/8" female NPT to 1/4" male NPT brass reducer. They are common at hardware stores, box stores, perhaps a well equipped NAPA, and even in the assortments that you can find in Ottterzone and the like chain stores. Just google '3/8" female NPT to 1/4" male NPT reducer' . Apply some teflon tape to the threads and be done.