The BTC 51xx-series dome-with-sliders keyboards have unique stabilisers that don't fit any keyboard/keycaps with stabilisers for Cherry MX. The wires clip into the case and slide in slits in the keycap: there are no stems or plastic clips.
The 2u keys don't even have stabiliser wires at all, only additional sliders on the sides.
In
this picture of inside a BTC-5139, it looks like the "Big-Ass" Enter key is like an ANSI Enter key with a slider in the \ position.
The shape of the keycaps is very similar to DCS.