well for starters I can see an awful lot of slack in the rear derailer cable in the picture and the routing isn't ideal, it should ideally enter the cable stop the same smooth way the front derailer cable does, looks like it's entwined with the rear brake cable, i'ld start with rerouting those control cables and getting the tension right. and I agree it can take some wrangling to get some of those wheels back in, I've found it helpful sometimes to pull the derailer towrads the back so it's out of the way of the freewheel.

we've got a police auction here this week and I'ld like to find a cool old bike like that.