Google: wheel adapters 5 lug to 6 lug
As you probably know all 5 lug are not the same size pattern, same for 6 lug, so you need to know what the 6 lug wheels came off of to get that dimension
Adapters are fairly thick, 2 inches at least
I believe Rangers are Hub centric, so the spacer/adapter is centered by fitting tightly over the hub, the lug nuts just hold the wheel on.
Other vehicles/wheels may be Lug centric, meaning lug nuts center the wheel on the hub when tightening them
You would need to measure the back spacing of the new wheels to see how far out they would be with the spacers you chose.
Also to see if you will have clearance when turning.
Look here for tire size and Rangers: Chart of maximum tire size
Read here on how to measure back space and other wheel dimensions: http://www.therangerstation.com/tech..._fitment.shtml