Radiators in an A-body?
I put an ECP 26" rad in my '70 Duster, I didn't look closely to see if the opening in the core support was big enough because the new rad looked to mate up fine, I doubt there's more than an inch on each side that's being covered by the core support. My old factory 22" radiator had big brackets on the side to reach the mounting holes and was visibly narrower than the opening in the core support by at least a couple inches, almost like the car was already set up to accept a wider radiator...? The ECP 26" radiator was pretty much a bolt-in btw, only had to drill an extra hole in each of the mounting brackets and another 2 for the shroud, very easy.
The core support blocking airflow will limit the cooling capacity a bit but the bigger radiator will still cool more because it has more fluid capacity and more surface area exposed to air (even if a small amount of that air isn't really flowing through the fins).