Hi Alex thank you for your findings. I am a little confused by the resistance reading between 11 &12 (slip ring and slip ring brush holder), I suspect the brushes and slip rings may be a little dirty causing the anomalous reading.
I would like you to check the connections on the new rectifier.
What I would like for you to do is undo all the lugs on the new bridge rectifier. Remove the four large wires, you can leave the two small black wires that connect to the rheostat. Using your multi-meter, on Ohms, put the black probe on 13 and then touch the red probe on all of the four loose wires, one by one. One of them should read 0.1 ohms. Connect this wire to number 2 on your new rectifier, along with the wire to the rheostat. Please check that this terminal has the sine wave symbol next to it.
This leaves you with three wires please use your meter to test between these wires, two of them will make a circuit with a resistance of 0.3 to 0.4 ohms. These two are the auxiliary field windings, the longer of these two wires should be the +ve and needs to be connected to number 7 (please check it has a + sign). The shorter of these two wires is the -ve and needs to be connected to number 8 (please check it has a -sign).
This will leave you with only one wire this needs to be connected to number 6, along with the small wire to the rheostat.
Now please check the resistance between 1 and 13 you should have a circuit showing around 4 ohms.
Bob