Two ways to do it.
One way is to simply remove both duals, then install the outside shiny wheel and leave the inside ugly wheel in the barn. Your stock tires have 3,970 pounds weight capacity each when mounted on a single wheel (not duals). So your rear GAWR would be limited to 7,940 pounds with one dual removed on each side and the rear tires pumped up to max (110 PSI?). That would result in a max GVWR of about 14,000 pounds, which is not much less than you have on a stock F-450 pickup.
Don't mess with the rear axle or the hubs, but you may want to replace the lug bolts in the rear hubs with the shorter lug bolts for SRW wheels.
But to do it right, so your pickup looks like an SRW pickup and not a dually with some tires removed, you need 4 new wheels with a 10-on-225mm hole pattern. Your stock wheels are 19.5"x6", but the new wheels could be 20"x8". Then you could mount the same tires the SRWs run, or LT265/75R20. With those tires, your 4.30 rear axle ratio would be an effective 4.02. Your speedo, odometer, and tripmeter would have a 6.5 percent error until you had the speedo calibrated for the taller SRW tires.
No need to change the rear axle or hubs. However, with 10-on-225mm hole pattern, you would probably have a real problem trying to find SRW wheels to fit. And the F-450 brake components are at least 1" more diameter than SRW brakes, so any SRW hub probably wouldn't work on an F-450.
If you want new wheels, then the answer is probably a custom wheel maker that can make you anything you can dream up. One source is:
Stockton Wheel Service - Custom Wheels
One option might be to have Stockton widen your stock wheels from 6" to 8". Then instead of your 225/70R19.5 tires, you could run "super single" LT265/70R19.5. That would give you a rear axle ratio equivalent to 3.90, and get you back to your stock GVWR of 14,500. The Drive-axle tires available in that size include Michelin XDE2+, and the all-position tires available in that size include Michelin XZE2+:
Michelin Americas Truck Tires
But warning: those super single Michelins are not cheap.
