So you are talking about the 385 equipped 67 Signet right?, with 3.21s, skinny14s, and a "mild" TC, right?
Well IDK anything about port-volume being an improvement.
But, IMO, in that 385Combo, as described, that factory iron intake is not the thing to change.
Ok sure, on the dyno, yur gonna see changes, but, that 385 is already overkill just as it sits, for the Signet chassis..... and
obviously, at the track, the difference will come out, with the appropriate gearing and TrapRpm.
But as a streeter;
I have a hard time imaging that at WOT, you could ever, on the street, notice any WOT-power change at all, from any change in any popular street-intake. I mean, top of First gear is like 50@5700 (if not spinning the tires), and on the shift, the Rs will fall down...down.....down; to where no aftermarket intake will make much of a difference. At 3500rpm they are all gonna be pretty close.
Back in ~1975, I put a 340 under the hood of a V200 wagon......... with a 2-bbl 318 top end on it from a 69 Satellite. I'll take a wild guess that your friend's Signet and my wagon weighed about the same. She was a high-compression tire-frying, screaming demon. And I imagine, so is a 385/Signet.
My current combo runs an AirGap, and I highly recommend it. But the engine has also run an X-cellerator, an AVS/iron, and a TQ/iron. All of them spun the tires thru two gears (A833) at least; so I mean, on the street,
it's like hunting squirrels with a shotgun.......
IMO; pretty much any intake on a 385 will do, cuz in a Signet, the gun is already way big enough.
But if you just want to buy your "older friend" an intake, well, don't let my testimony stop you, lol; there's plenty of choices out there, that will spin the tires all the same.