Well once I got the soldering iron out all bets were off on getting this job done and dusted quickly.
I took off the casting by wafting a micro blow torch across the joints, because my soldering iron doesn't have the thermal capacity to cope with large conductive surfaces. I added a shim to the floor so that the casting bracket would not be floating at an uncontrolled height from the floor when I re-soldered them back on.
I also chose to file the cow-catcher where the bottom Kadee box would fit, but even in spite of doing this, I ended up having to cut off part of the lid on the box, so that the coupler would fit as you see above.
All back together and a comparison between before and after modification to get the Kadee coupler box to fit.
And here is a side view showing how much lower the cow-catcher is. Unfortunately the coupler is drooping, which I suspect is down to the missing lid.
However, the height is in the right ball park when the assembly is checked against a height gauge.
Uhm... not totally 100 percent happy with this. So for the next one I'm going to increase the shim thickness so as to lower the cow-catcher casting a little more, as it appears I will have enough clearance for it not to short on the track.