OK. Another option is Kaydee which will couple quite nicely to Accucraft. They make an offset coupler with a rise that might get you where you need to go without hacking up the tender, but sometimes desperate times call for desperate measures like for my Bachmann Porter…
(http://lsc.cvsry.com/post4/PorterPilot-01.JPG)
The Accucraft coulers also have a hole up through the rear of the draft gear box that can accommodate a bolt or screw to hold the pulling force, then the little hex caps are just for show.
Here, on the rear of my Porter after cutting a hole and raising the floor, a bolt down from the floor is the primary attachment, I trimmed off the top two holes on the surface mount and used Phillips head screws because I didn’t have a hex driver small enough…

The best advice I ever got about installing couplers was “do whatever it takes to make it work” Of course, if you are worried about resale value of your models then you might need to consider alternatives.