Well I finally replaced my broken camera and have taken photos of my conversion These engines are GG1 chassis with EF58 Japanese Electric shells on them.
Garth, Try cutting the outer most pin(heat welded pin that holds on brass plate) on the brass plate with an xacto knife, lift it up slightly, remove marklin coupler and spring and replace with micro trains coupler and spring a very tiny amount of crazy glue, i usually use a tooth pick and put it on pin from outside(not the pin where the coupler is secured). I have done a dozen or so this way with no problems so far.
I've done the same thing on Marklin rolling stock or locos where I want a MTL coupler. Works great and is easy as long as you don't go nuts with the CA.
interesting conversion, but as Loren mentioned, #901 and #902 couuplers would have been easier. Al my DB Märklin locos have these. Or did you have a particular reason to use the #903?
I found the 901 902 were easy to install but difficult to close the box again after installation of the coupler, I found this a much more stable and satisfying option plus I favour body mounts over talgo trucks. In addition all the Marklin stock I have left have been modified to MTL trucks and couplers none have 901 or 902's any more. just personal preference and what works for me. someone had posted wanting to see how it could be done and I could not find the ir e-mail or the original thread so that more than anything prompted the post.
I know how to do it this way and was not always happy with the method or the coupler action and I have most of my carsand engines with body mounts. A drop of AC or craxy glue from a toothpick is a good anti rotation device for Body mounts.