Are you guys sure the MR version actually comes with electrocouplers out of the box? (since the parts are all the same, I'm pretty sure the same exploded diagram is used to represent all of these engines, whether they came with electrocouplers originally or not)
I'd trust the scanned manual, I think that's more likely correct for this model's vintage.
My memory may be slightly off (since it's been almost 23 years now ), but the very first few GP9s of this series did not come with electrocouplers, but they did have the ability to add them via the kit.
The first few were NYC and Southern Pacific (part of the freight sets that included the CAB-1 remote, and possibly available separately later), the Pennsy, and this Milwaukee (maybe another I am forgetting). I think some of these earlier ones didn't come with electrocouplers out of the box.
Then there was the Canadian Pacific, the Lionel Centennial, A CB&Q, and some others (like the UP in the ore car set - which may be the one pictured in the diagram). These later ones I believe were cataloged to have the electrocouplers. The Centennial one specifically, I know they goofed and did not include them, but Lionel made good and sent electrocoupler kits to those who purchased the engine at no charge since they didn't ship them that way.
I have a Milwaukee Engine somewhere, but can't check it right now. (There's also no guarantee I'm going to have time to go look for it in the near future - sorry! )
Food for thought. If you aren't making your purchase decision specifically based on whether electrocouplers come with the engine right out of the box, then it doesn't matter much. It sounds like you would be OK with it if you have to add them yourself. It's also quite possible a previous owner added the kit already(if my memory is correct and MR didn't have them straight out of the box).