RicksonTruck.com sells a direct replacement 8 lug rim for the Ford, Dodge, and GM 16" rims, with 17.5" dual wheel configuration. I don't know if they have them in single applications or not.
You can call them. Probably they will have a 9/16" hole, that is what was on my 1975 F-350 SRW supercab truck.
17.5" rims are going to have a much higher weight rating. Even E load range will be much higher weight rating than a E load range on a 16" rim. Check the load ratings, to see if you might need F or G or H load ranges. Rickson can get the 17.5" tires, but your local tire shop should have a better price including shipping. What is on Rickson's website are not up to date prices, as oil and rubber prices change monthly so do tire prices.
Good luck on your purchase. You might also contact Mobile Suites. They probably are able to tell you the supplier name on the 2015 trailers, and they might be able to supply you with the correct 17.5" rims that fit your bolt pattern.
Another source might be [www.etrailer.com]eTrailer.com They also sell replacement rims and brake systems. Many who have changed to disk brakes find it re-assuring that the brakes are now very effective - once disks are installed!
Good luck
Fred.
