There were two hulls used by the Circus Circus team in 1989. The primary was hull #8700 (Newton 158). The key features for 1989 were Jones sponsons, inset transom, short cowling nose and it ran with Jones verticals. The backup hull was #8401 (Newton #146). This hull had Lucero sponsons, flat transom (with small supports for the verticals), a long nose and both Jones and Lucero veticals.
It sounds like you are making the 1989 primary hull. The pictures that David has of the 1988 Circus Circus are of the 8700 hull (inset transom is the key), and are a great resource. I bought a bunch of them and they are great.
Rick