Using an adapter is not the ideal situation as the air doesn't have a straight path into the plenum areas. Square flange intakes also have smaller plenums that spread bore intakes.
It's far worse on factory four hole intakes. Aftermarket intakes typically have two big openings so the incoming air isn't slamming into a "shelf". Despite the miss-match and smaller plenums a lot of folks use adapters with good success.
Most of the time they are adapting a square flange aftermarket carburetor to a factory intake following the trend to get rid of the Quadrajet and install a "high performance" carburetor instead. Even though more times than not they would have made more power with the Quadrajet they removed, I still hear that sentence regurgitated over and over.
Last time I looked it was 2022, and you'd think folks would be a LOT smarter these days.
Anyhow, there are several different varieties of adapters out there, most are apprx 1/2 thick. Make sure that between the height of your aftermarket intake plus the spacer and gaskets that you have adequate hood clearance. I'd also make sure that your adapter has a divider in if it is the fully open variety. I've seen issues with those causing a stumble/hesitation/bog going quickly to full throttle with some set-ups. Mine was one of them. If I tested any sort of spacer under the carb to my dual plane intake the car would NOT go from idle to full throttle with good traction without stumbling. Remove the spacer or put a divider in it and the launch was flawless.
I suppose with some engine combinations they don't much like a lot of area under the carb open to both sides of a fully divided intake.......
