Headers won’t fit in 67 440 dart

I can't tell which parts you are using from the picture. Maybe tell us which K frame you have and which motor mounts you are using. Are you trying to lift the engine and K frame in from the bottom while they are attached to each other? I'm not sure that will work but that is what it appears that you have bolted together.
What worked best on my Duster was to lift the engine and transmission into the car from below and then to use a transmission jack to lift the K frame into place.

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