Many kits tooled in the 1960s for both pre-assembled dealer promotional use and assembly kits used a one-piece chassis pan. You can just paint it flat black and be done but replicating a factory-fresh appearance adds a nice surprise when flipping over the model. I painted the Phillips-head assembly screws to match the surrounding surfaces. Ambitious kitbashers may want to investigate substituting the chassis/suspension/engine compartment of AMT/Ertl’s 1966 Oldsmobile 442 kits for added detail.