The V and Z transformers were mostly the same and are covered in the Postwar Service Manuals that were put out by Greenberg and others. These include wiring diagrams, parts lists, and an illustration of assembly. I would focus on the transformer core and determine if it is usable. If it is, then worry about the rest of the unit. The rust on the laminations is unfortunate, but not much you can do about it now. Clean it up with a wire brush and move on.
Identify the 120 volt coil input leads. Clean the voltage tap windings on the core with a fiber brush. Do not abrade these exposed coils, just clean them so there is nothing shorting the individual wires. This is the area where carbon rollers run. Then identify and isolate the individual coils. This can be done with an ohm meter to separate all the leads into coil pairs. There are three separate coils wound onto the laminations. The primary, 120 volt coil (two leads), the minimum voltage 6 volt coil (2 leads), and the 6 to 24 volt variable voltage coil ( one lead and the one of the exposed variable voltage wires).
After identifying and isolating all the leads, connect approximately 15 Volts AC to the 120 volt coil leads. Then check the other two coil pairs. The 6 volt coil should have about 1 volt on it and the 6 to 24 volt coil should have about 3 volts on it. Be careful doing this. If you have misidentified the 120 volt coil, you could get as much as 200 volts on some of the coil leads. If this checks out, then connect an unplugged power cord to the 120 volt coil with a 4 amp fuse in series with one lead. If you are not comfortable with working with 120 volts, tape up all the exposed connections. Plug in the cord and check with a volt meter that there is no voltage between either of the 120 volt leads and the steel laminations. Check the voltage on the two low voltage coils, they should be at 6 volts and 18 volts. If they seems to be working, unplug the test cord. If the 4 amp fuse blew, give up on this transformer. If you have the means, the next thing to do would to be to put an amp meter in series with the 120 lead. With the coils energized and no load on them, the transformer should be drawing less than 1/4 amp. If it is drawing more than this, give up on this transformer.
If available to you, the next thing would be to use a Megohm tester on each of the three coils. I would use the 250 volt test between each coil lead and the steel laminations. It would be nice if the Megohm test would provide results greater than one megohm. If it less than 1 megohm, you will need to decide if you want to use the transformer or not.
If these tests show that the transformer coils are good and the insulation is good, then clean up the rest of your transformer and reassemble it using the service manual as your guideline
