The adapter Lionel produced to hook prewar and postwar cars together is the TT-100 and TS-162:
You can also remove the shell (careful not to break the retaining tabs off) and replace the trucks for postwar trucks. Lionel did that for some of the first locomotives of the postwar period such as the 221, 1654, and various scouts. You may actually find it more cost effective to find one of these postwar stamped metal tender that has the trucks and coupler you desire.