For the most part, these are pretty rough castings that will need some serious TLC. It looks to me like the master was molded pretty quickly. They stripped off the undercarriage greeblies, built up a base of clay or wood, then just dumped rubber on it. The mold was slit, and castings started coming out. The detail on the underside is terrible. TONS of pits from non-degassed rubber. One of the castings looks like it was cast in a pressure pot, causing the resin to expand INTO the air pockets in the rubber.
While they will require some work, these are overall pretty nice pieces. A little love and they'll be great.