Can't help you with the mismatch issue, but if your intake has the "hot-slot" like the one in the photo below (that's an intake for a Holley, but the same "hot-slot" design was used on many cast-iron Q-Jet intakes), I recommend plugging the holes at each end of the slot with core plugs as shown in the photo. That slot is connected to the exhaust crossover passage, and allows hot exhaust gases to heat the carb base at cold start for improved atomization of the air-fuel mixture, with a stainless steel heat baffle to protect the carb base from direct impingement of the hot gases. Unfortunately, that heat also fries/distorts the carb base and can cause the bottom well plugs to fall out of the Q-Jet float bowl, resulting in engine fires. GM recalled millions of Q-Jet-equipped cars with this "hot-slot" design in 1969 due to the fire problem, and abandoned the "hot-slot" design in 1970.
What's the casting number on your intake?