Some times you have to sneak over to the other side of the road to find info. Checking over on the Ranger Station shows that the Explorer 8.8 is 59.5 inches wheel mount to wheel mount. It gives other info on the rear that one may or may not need too.
https://www.therangerstation.com/tec...lorer8_8.shtml
The stock bed is 50 inches inside or about 50-1/8 on the outside Personal experience says 1/2 inch clearance isn't near enough.
59.5 minus 9 for a 4.5 back space leaves your rims less than 1/2 inch from the bed sides with no tires.
You can play with this chart and figure out what the width of a tire should be on a certain width rim
https://tiresize.com/tiresizes/265-45R20.htm You have to plug in your correct size but it is a handy tool for what you are trying to do.
I'm not a fan of spacers but the ones that Jweb suggested are the way I would go. They seem to do a lot with the pro touring brigade and a few searches lead me to them almost every time.