Swapping a quadrejet for the same model quadrajet, snag, please help!

[MrSchaeferPants]

Ya w/o knowing which Q-jet we'd just be guessing. Geezer's right on about the brake booster, the port on the back, or the one in the back of the intake mannifold.

Your front left or driver's side port sounds like a mannifold vacuum source, where it's a 71 I'm assuming your dist runs on mannifold vacuum. You can switch the tubes if they're the same diameter, plugs if they're the same size.

About switching your lines around, if the line on the passenger side you speak of is ABOVE the throttle opening (or towards the TOP of the carb) then no, that's a ported manifold source, whereas your original carb sounds like your engine/distributor uses a manifold vacuum source (towards the BOTTOM of the carb)

And I'm going off of what I know about 4M Q-jets. No idea which one came on a 71