The original voltage regulator used on the early 8N was Model VRR-4008-A. The terminal tabs are marked with a 'B' (battery); an 'A' (armature); and an 'F' (field). The model number is also stamped on the base by the A and F posts. Look closely at the ARM and FLD tabs and you can see the 'A' and 'F' thru the screw holes.
Tim Daley(MI)