You'll be fine hooking it to the upper port. If it turns out to be manifold vacuum when the engine is running, then that's what you'll have to run. It's not a big deal. Good luck. John.
1968 Chevy C-10, 250 and 3 speed on floor, Hedman headers, Offy intake, Edelbrock 600cfm 4 barrel, HEI
1966 Chevy C-10, motor and tranny went into the '68. Waiting to be restored.
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