Just adding my 2 cents here. I drive a current era school bus daily. Each of the buses I've driven for my employer still use a straight axle and parallel leaf springs. The non air brake versions use 4 wheel disc brakes (and 10 bolt semi wheels). They also have power steering.
If you truly want an IFS, look at early 60s big bolts. Our 1962 fire truck (it is a C-60). I was honestly surprised to see that it came with an IFS. I always wonder why if an IFS is so great, why did GM switch back to a straight axle?
