layback,
215 75R16 has a narrower rim width (and narrower tire/section width) than the 245 75R16
Both have about a 30" diameter (which will be "taller" when mounted on the narrower rim).
The narrower 215 75R 16 will be a better fit on an original relatively-narrow wheel.
That size tire is readily available from a variety of manufacturers.
The question about using/needing a tube is probably regarding rims that might leak air.
There are supposedly no radial truck tires that allow/specify tubes. Some people (tire pros) have posted that warranties are voided if you use tubes in tubeless radials. My dealer installed tubes in one set of tubeless radials and told me he would honor the warranty.
