[mikethedruid]

First, you are going to need to make a new back for the radio. You can do this easily enough by gluing several layers of card stock type cardboard together, 4 should be enough depending on what you use. One good and cheap source is the front and back panels of large cereal boxes if they are big enough. If not, go to an office supply store and buy a couple of sheets of the white cardboard type poster board. Whatever you use cut 4 pieces the same size and shape so you can easily stack them, and larger than the backside of the radio. Next glue the sheets together with 2 part epoxy glue. Spread it on liberally between the layers all over. Stack the sheets with glue between each layer but NOT ON THE OUTSIDE of the bottom and top layers. If you use cereal boxes make sure you have the UN-PRINTED side of the card stock facing outward. Put a piece of newspaper below the stack, and one on top of the stack, and then put a piece of plywood or a large book big enough to cover the whole stack on top of the stack and paper covering, and add more weight, more books or the like, to press the sheets of card stock together while they dry. When the stack is dried well, remove it, and then spray it with polyurethane on both sides to help it resist water and moisture. When the poly is dry, then put the radio on top of the stack, back side down, and trace all around it. Cut out the back just to the inside of the line you traced so it will fit nicely into the little edge on the back of the cabinet, using an Exacto knife. Then, using the Exacto, cut ventilation holes near the upper part of the back and near the lower part of the back to allow air circulation to dissipate the heat from the tubes. Also cut a slit for the power cord, and an oval hole over the place where the loop antenna socket and external antenna wire come out of the back of the chassis. That will get you a good, workable back for this radio.

Now, as to the antenna loop, here is a link which describe the process of making one which you can then attach to the new back you just made above...
http://www.sparkbench.com/loopante2.html
Once you make it, run a wire from each end to the two terminals of the plug on the back of the chassis. One of these wires will be permanent, one may not be. Test the radio. If it seems weak, remove 1/2 a turn but do not cut what you removed. At this shorter point reconnect that wire, see if it improves. If it does, keep removing 1/2 turn at a time, until you find the ideal length. The cut off the excess you removed, solder the connector wire, and that's it. Just glue the loop to the new back.