There are a handful of 760 mm lines still using the "rollback" system designed by the Swiss to handle standard gauge cars on narrow gauge track. I think that both the Zillertalbahn and the Murtalbahn in Austria continue to interchange freight traffic this way. Up until recently, the Harz Mountain lines in Germany also used transporters.
There's a very descriptive You-Tube video demonstrating how the JHMD (Jindrichohradecke Misini Drahny) Railway in the Czech Republic moves some pretty hefty standard gauge cars over its 760 mm line. The You-Tube video shows JHMD's diminutive diesels (including a mid-train radio controlled DPU) on a freight. Search for "JHMD Freight Trains" to access the video - which shows exactly how the "rollback" trucks are employed.JHMD is 80 km long, operating over twi cubes near the Austrian border. It's an impressive operation that continues to use steam on summer passenger excursions.
A few years back I rode a mixed train on the Zillertalbahn to Mayerhofen where we were to ski. The train's narrow gauge coaches were trailed by three or four cement cars on transporters. The top heavy cars rocked back and forth as we rolled along at a good clip a. I recall yhinking we are going to fip the standard gauge cars - but nothing happened. It was standard practice on this private narrow gauge.