Nice looking bus!
Having a flat floor makes building a conversion that much easier.
Does your bus have air ride suspension in the rear? If so, that will make for a much smoother ride than if it is on steel springs.
I don't know if it is the angle of the picture but it appears as if the rear tires are a smaller diameter than the front.
It is relatively easy to build some blocks to raise the rear of the bus up high enough to put the same size tires in the back as in the front. By doing so you will increase your top speed 5 to 15 MPH.
Having the same size of tire makes it easier to find tires when you need them.