M A Cotter MK-2 transformer differences?

Think they are just for different impedance cartridges. I have a "verion" P (predessor to him calling the company cotter) that was meant for 3 ohm cartridges. All the models are re-wireable to other settings (plate where hook-ups are comes off & reveals 9 or 12 pins which are jumpered to create specific impedance)My verion is also blue and appears identical other than brand name. Think he OEM'd it to Bryston for awhile too

I may have the jumper diagram somewhere, don't think unit had a manual, you just bought the version applicable to your cartridge, plugged cartridge into transformer & transformer into phono in. The screws to take it apart are under the rubber feet (hex?)Pull the screws out & unit slides out of blue sleeve. Nothing to really look at though, just a sealed epoxy filled steel shell. Pins are accessible by taking end plate off (ins & outs)