I purchased the engine with Merkur couplers. By removing the two red-yellow front and end boards, I got easy access to the nylon coated metal nut that holds the coupler and replaced it with Bing couplers. I choose Bing style couplers, since they can also couple with Lionel latch type couplers.
The Merkur engine is a heavy weight of 23 cm (9 inch) length, it can both crawl and run. It has no sound system. The motor sounds a bit like a vacuum cleaner when it races over the tracks. The engine has directional lighting, runs smooth and pulls a heavy consist with ease.
Here is the new control centre, with toggle switches for AC/DC and DC direction. Furthermore, it is equipped with an automatic short circuit safety system and many switches for lights and future uses.