John,
Look no further than our "tech tips" department for a complete explanation of how intake heat can help your 250 run better. You say you are running the original carb with "dual exhaust manifolds". By that do you mean a split exhaust with the heat stove removed? If so, you need to restore the heat to the intake. You can buy a hot-water box from Stovebolt Engine Co. or find them on EBay.
The condensation on your carb is normal and just confirms that you have a cold air/fuel mixture flowing into an intake manifold that now has no way to heat up the mixture for better distribution, like the tech article mentions.
By the way: a "Swamp Cooler" was a big ugly window-mounted cannister that forced hot outside air through a wet filter element to provide a crude form of air conditioning. They can still be found at swap meets, but they don't work very well.
