[Arran]

Ron;
  Bob Andersen made a restoration series for a 37-640 a while back. One interesting thing that I learned from his series is that you can actually dismantle the chassis by undoing those hex headed screws on the top and sides, and by undoing a bunch of wires connecting the sections too of course. So if lets say you wanted to strip the rust off the IF side you can remove the top section, dunk it in evaporust or whatever, and then put it back without disturbing the rear apron with the stickers all over it. In his case he had to derust everything, and replace almost all of the tube sockets too, but apparently evaporust doesn't harm brass or aluminum so you could leave them in place whilst derusting the chassis parts.
 I don't particularly like the design, I think that it added complexity with little to show for it, but I can understand why they thought it might aid production. I think that the idea was that they could make common sub chassis that would be shared across different models, the IF section would be shared across everything from a 37-610-640, the RF deck in everything from a 37-620 on up, and the power supply and power amp sections could be shared between the 37-620/630, and the sheet metal stampings were all the same of course. On paper it was a good idea, sort of like the modularity of a desktop computer, but of course it was all hardwired, and in the long run it may have saved some time but used more materials, like those hex head sheet metal screws for one, and they had more parts to manage and inventory.
Regards
Arran