if it were mine i would figure 200lb x 66 which would be 13,000 not including the empty bus weight. (like if i were hauling heavy kids ...
), so your total weight will be less than that. anyway, that chassis/engine combination hauled 28,000 lbs in one delivery trucks that my dad had back then. the thing should be running at least 900x 20 tires...10's would be better.
with that weight, it won't take off real fast, nor go up hills real fast, but if it has a 2 spd will drive fine or most roads.