With 1" spacers, I simply had to cut the unthreaded end of the original studs (3 or 4 mm).
If we analyze the stresses supported by the bearings, we see that adding spacers only increases the stress on the inner bearing, which is the one that wears the least.
My 285 x 50 x 15 wheels mounted on 8" rims are wearing steadily so far, but I've only covered 1,600 miles.
It's true that the maximum recommended width with 8" rims is 275 mm, but if abnormal tread wear occurs, it's always possible to adjust the inflation pressure accordingly.