You may want to check out the Vintage Photo Archives
to see other examples of 1977 Sovereigns
The folding part & dimensions sound appropriately original...it should fold flat to make into a bed. However, the different fabrics may not all be original. In the older trailers, things get modified for various reasons...oh, if only they could talk!
If you could post a picture that may help, someone here that is more familiar (than me) with that particular era could help.