The problem I have with swapping to something else is that I love the look of those old 18 inch dually type wheels.
I'm trying to find a way to modify the wheels, probably move the centers to a smaller wheel, to keep the look and run smaller tires.
One of the things I did today was look for 16 inch tires to fit one of my cars. I've pretty much decided the best solution is to buy 17 or 18 inch wheels. Seeing you needing to go the other way made me chuckle. Performance car tires are a whole different game than tires for old trucks...