Iron 273 4 barrel manifolds

Your question is about the intake only. My guess is you could get a massaged 273 intake to run quick enough to need a roll bar in an A body. I have come to realize you can make WAY more power with a massaged stock intake than most people think possible. Aftermarket better? Sure! Absolutely! I have seen 560hp out of a massaged 383 intake. I’m about 400 through a massaged 68 340 intake. All through stock exhaust manifolds. If you have a SERIOUS stroked short block with SERIOUS head flow. A massaged stock intake will flow a BUNCH! The more depression you have at the intake port of the head, the more the intake will flow. Remember air is drawn into the motor. The first air to move is at the back of the intake valve. Something to think about, say you were running a blow through supercharger. Is the intake an overwhelming concern? High boost or high depression can overcome a good number of warts an intake might have. These are very broad/simplistic statements, but I feel if you are looking for the bottleneck in an stock casting LA motor it is head flow, then exhaust, then intake.