Thanks guys for your help, but it appears that Cat did this little different.
For me it appears that the track housing slides under the x-frame and there's some guide rollers on the side
(some of it can be seen on the pugs video link)
In the first picture you can see that the 374 is narrowed for transport, and in the second it's wider.
It's a little bit confusing cause there's seems to be some differences between the 374, but if I understand correctly the Variable Gauge Undercarriage is standard in all 374.
There are plenty of pictures of the 374 in action but naturally the undercarriage is often so dirty you can't see too many details on them.
