I am guessing this is on the 50 1/2 ton you list in your profile?
If so, do you already have the bed on? If the bed is on the frame you can bolt the splash apron to the runningboard and then install as a unit. Or, install the runningboard first then install the splash apron. The splash apron will fit with the running board in place, just be careful not to scratch the paint. You can do it either way. Don't forget there is on bolt hole on the splash apron that will bolt to the rear fender.
Good luck!!
