Your friend's 19.5" tires and wheels are not worth it for your dually, for many reasons.
1. The adapters to go from your 8x170mm bolt circle diameter to his 8x225mm bolt circle diameter are $350.00 a pair. So there's $700.00 spent on 4 adapters.
2. These adapters are dubious at best, in that they are not OEM engineered/produced.
3. The adapters are 2" thick, which will add tremendous leverage on the hub's wheel bearings, virtually guaranteeing early failure at substantial cost... unit bearings are $$$$.
4. The offset change could effect handling, steering, GVWR capacity, and safety.
5. The adapters do not have a hub land! The stock 19.5" F-450 steel rims are made by Accuride, and are designed to be center piloted by the hub, not the wheel studs. When mounted onto adapters without a hub land, how will the wheel be centered concentrically to the hub and rotor assembly? It won't. Period. The center disc to the Accuride wheel is flat, which means it offers no truing seat for conical lug nuts that stud piloted wheels have. The OEM lug nuts are swiveling, because wheel centering occurs at the hub pilot land. Without wheel centering... a fred flinestone ride is what can be expected. Along with more accelerated, choppy tire wear.
6. An F-350 dually truck has all the tire capacity that it's maximum GVWR can use, and then some, with 16" Load Range E tires. It's one thing for single rear axle trucks to switch to 19.5" tires and wheels for heavy resident loads like truck campers. But wiith dual rear wheels, there is already the potential to have 12,000 lbs of tire capacity on the rear axle alone with the stock size 16" wheels and tires. There is no real world benefit, other than looks and misguided bragging pretense, to fitting 19.5 tires on a truck that already has dual rear wheels, but doesn't have the spring capacity or the axle capacity or the frame capacity to handle more.
7. It is FAR easier to obtain 16" truck tires, with more variety, greater selection, at more places, and at cheaper prices, than it is to obtain 19.5" tires.
8. Quality 19.5" tires cost between $250 to $425 each, depending on the tire and where bought. I paid $339 each, for the 19.5" tires in the stock OEM size on my F-550. And I checked EVERYWHERE, online and offline, for the lowest price. I ended up special ordering them thru Costco, who had the lowest price, but who also refused to mount them, as it is their policy not to mount 19.5s. Compare that to the variety of 16" truck tires that Costco, and every other tire store imaginable, keeps in stocks, and mounts without issue every day... all for as little as $109 per tire, up to about $189. Hmmm, $150 versus $350 per tire, where the less expensive tire is more than adequate for the GVWR of the chassis? And where the less expensive tire is more immediately available for emergency replacements? And will be mounted without balking? The winner is clear.
9. The 19.5" tires have steel cords in the sidewalls as well as the tread, making them quite durable when aired up, but quite vulnerable to zipper failure if NOT aired up. A partially deflated tire bends the steel cord in the sidewall back and forth over 38,000 times in just ONE hour of driving. Imagine taking a thin steel wire and bending it back and forth 38,000 times. Like an aluminum can, it is going to fatigue and fail. Break in half. That's what running low on air can do to a steel corded sidewall tire (19.5's) that it will not do to a tire that doesn't have steel cords in the sidewalls (most all 16's, with the non-relevant exception of two $380 ST trailer tires in load ranges G and H).
10. The bead taper of the 19.5" rim is much shallower, at 15 degrees, than the bead taper of your 16" rim, at 5 degrees. So if for whatever reason you DO want to "air down" your tires for driving on sand or what not, you can do it with more probability of retaining your tires on the 16" rim with the steeper 5 degree bead taper than you can with the shallower 15 degree bead taper of a 19.5. Not that you have need to do this at all, but it just represents one more thing to think about when it comes to evaluating if the swap is worthwhile for you.
11. Almost forgot... most 19.5" tires are speed rated to only 75 mph maximum. The only two exceptions I am aware of are the old (and discontinued, and certainly not missed) General LMT400 series, which were speed rated to 81 mph, and are likely the tires that your friends F-450 chassis cab came with originally. The current Continental HSR and HDR series of tires that are the OEM fitments for both the Ford F-550 and the Dodge 5500 are speed rated to 87 mph. This is one of the key reasons why these tires are fitted as OEM, according to the press releases where Continental gloats about the OEM's selection of their 19.5 tire over the offerings of Michelin, Goodyear, Bridgestone, etc, which are all speed rated to only 75 mph. This is really key, as some lawful speed limits are 75 mph, and in those areas, it is not unreasonable to expect drivers to move along at speeds of 80 mph or higher. It doesn't effect me, as I tow at 55 mph, per the law in my state, so I am satisfied with a tire limited to only 75 mph. But if you find yourself exceeding 75, then your choice of currently available 19.5" tire is limited to the Continental HDR and HSR. Whereas there are many 16" truck tires that are speed rated higher than 81 mph.
For my F-550, the 19.5" tires and wheels are appropriate. The much thicker frame, the much heaver Dana 135 axle, the much higher GVWR capacity... all support the need for a higher capacity tire... and the much larger brake rotors that came with my truck accommodate those 8x225mm bolt circle diameter wheels on the hub pilot, as engineered by the OEMs.
For your F-350, making the switch, even if the tires and wheels were GIVEN to you, would cost you more... not only in dollars, but in safety as well. I'd pass it up.
