I know ranger/Mazda beds are interchangeable other than taillights and body lines being different. Are just the 4WD fender flairs/trim the same or are the wheel wells different, any difference, if any, is too hard to actually see.

 

Yes, the Mazda B-series beds are a different design on the exterior, but as far as wheel wells and tire fitment they are the same as Ranger style side, Mazdas never had the "step side"(flare side)

Mazda fender design seen here: https://crdms.images.consumerreports...B20MAT081A1112

Rangers seen here: https://static.cargurus.com/images/f...-1024x768.jpeg

The lines look to match up but the wheel well flares are quite different