I have drilled out the tension lock coupler from the brake van bogie which is not really needed anyway. After a lot of fiddling about I have found that a medium centre set whisker coupler # 148 gives a perfect fit on the coupler. The height is correct and the back of the knuckle lines up with the buffers. Even the hole left in the bogie after drilling out the rivet is the same size as the hole in the Kadee coupler ; it takes an M3 hex head X 5mm screw. Unfortunately, the nut is too big and rubs on the underside of the coach. The head of the M3 nut is also too big if I try and reverse it. I will experiment with some half nuts and try to find some M3 screws with a smaller and flatter head. I have nothing on hand at the moment but I am sure an ebay search will turn up something.
These look good :
https://www.ebay.com.au/itm/50pcs-M3-x-5mm-Laptop-Notebook-HDD-SSD-Screws-Phillips-Wafer-Flat-Head-Screw/272395915421?epid=908794100&hash=item3f6c0fd09d:g:7cUAAOSwCGVX7h9P
Almost there.... !