Most on here have played with pickups and big bolts (same cab as a pickup) or COE's but a school bus is a bit different because of the long body. Look at it closely, I think there are 2 main options,
One possibility may be to carefully lift the whole body off the frame and drive a new one under it.
Another way to do it is to replace springs and axles (leaving spring perches in place is preferable) and then replacing all the other drivetrain components with newer counterparts.
You are the one doing the work and know the extent of your abilities and availability of friends to help!
