After having supply problems earlier in the year with the innovative cast aluminum crossmembers on its new minivans, Chrysler Corp. reportedly has reached an agreement with The Budd Co. to supply conventional steel crossmembers. It is not known if the steel will be used to replace the aluminum versions or will simply be used as an additional supplier -- nobody at this point is talking. One other theory is that the steel units may only be used for a few special models. Budd reportedly is setting up the steel crossmember fabricating equipment at its Kitchener, Ont., plant.