Intake manifold for 225 slant 6

The 2bbl will improve driveability, performance, and mileage quite a bit if the swap is done correctly and thoughtfully; AJ/FormS' experience is not typical; clearly there were other problems with that car that didn't get addressed.

The pre-'67 cars make special issues because of their rotating-rod throttle linkage. When Super Six cars were plentiful in the wrecking yards, the easiest path was to swap in a cable-type accelerator and associated linkage. Those cars are now all but nonexistent, so you may want to proceed otherwise. See the parallel 2bbl setup article. Photo documentation of a very well done such conversion (on a '62) is here.

Yes, the stock undersized exhaust pipe is a bottleneck you'll want to address sooner or later. No, it does not determine whether or not your 2bbl swap improves things.