15x8 w/3.75" backspace question

On the Back I once installed 275/50-15s, on 8.5s with 3.75 bs; so I think your 8s will be ok. I later installed 275/60-15s on those 8.5s and they still fit...... after I moved the axle back a bit.
My car is lowered some, so they had to be IN the tubs.... at the top. and the front needed a tad more clearance at the rockers.

The 15 x 7s will work on the front as per the recipe from @autoxcuda