Just like the front frame, the RCR replica comes with a number of aluminum sheets and pieces that provides a rear sub-frame. Very functional but not period-correct. Time to fire up my CAD program and welder. 

I used the bottom sheet provided with the kit as a basis for my design. I know I am probably adding 20lbs in weight but it is more about appearance than building light. My steel frame duplicated all the attachment and pivot points on the stock rear structure.