Yes they will work on F-350's. For a 1999-2016 it is part number: 75403-01A
For a 2017-up: 75413-01A
There are not different size steps for the Bedstep2
In between the cab and rear wheel. Here are the install instructions for the step you need, https://sharptruck.blob.core.windows.net/webdocuments/IS-75407.pdf