The numbers are on the US passenger side of the transmission on a vertical surface just above the pan mating line.
I have some photos at http://photos.yahoo.com/tabijan
in the 722tranny album. This is a tranny off an 81 300SD but I doubt yours is much different. You can just about read the numbers if the full size option is available to you. Doesn't everyone keep a junker tranny in the garage for photo ops?
And since I'm a stickler :p an 86 500SE should have an M117 not an M119 even if I know you have an M116 so it doesn't matter