I'm waiting on a 5140 to arrive by mail and rather than try to source an extra Ctrl key for a symmetrical 60% build I was considering incorporating the compact keys into one of the LF PCBs. Here's the unique layout of the 5140:
And here's an example build of the LF78 in one of their cases (it's a skinny boi):
So I think the footprint of the compacts is still the same as SKCM switches (?) in which case I'd just need a custom plate to mount it . I'll probably axe the Scroll/Num Lock keys and put the Esc key in the right legend.