Why do you want a 20 pin Saturn? Have you got a 20 pin mod that you want to (re)use?
I can only help you with the model number from a Euro Model 1 (20 pin) Saturn, and I'm guessing that won't be much help.
MK-80200-03
BTW, a Saturn with oval power and reset buttons is a fairly safe bet as far as 20 pin Saturns go. There are such Saturns that are 21 pin, but they are definitely in the minority.