Nice... 15x8 fronts with 4.5 bs, 15x10 rear with 5.5 bs... this combo should be a-ok for fitment. Tire diameters will determine fender clearances. (You could go to 245-60 easily for the f). 275-60 rear is a tall tire... may have to flush the lips, maybeeee a slight ~1/4 spacer for clearance from the leafs. You could also try the BFG 295-50 for rear.... or else, just have 15x8 f/r... 245-60 f, 275-60 r.
I use 15x8 f/r minilites with ~4-3/8 bs, pushes the rim out ~1/8 ",.... 255-60 f, 275-60 r..... street/hwy cruising setup.... very good ride/comfort/handling.