Hi Peter, having the lock on the head side was a safety concern of mine as well. In terms of a shoe in a hole like you described, might not give me enough bite on the dovetail without using excess force. My cross slide is 13.5" long, so notching it out 1" or so for the lock shouldn't reduce the overall strength or integrity of the unit.
My cross-slide is 14" long, longer than yours by 1/2". I wouldn't worry about the lost length either. Mine has a very simple allen key grub screw that bears on the Gibb which is on the tailstock side. The grub screw is flat while the Gibb is sloped at that spot. So the grub screw grabs tightly. But I don't like it. I'll probably either make a tapered (cone shaped tip) Gibb screw or notch my Gibb with a flat in that area. I kind favor putting a flat spot on the Gib. That way, there is zero chance of messing up the bearing surface on the Gibb with screw marks. Less chance of moving the Gibb as the lock screw gets tightened down too. And last but not least, a new Gib would cost WAY LESS than a replacement cross slide.
So ya, I lean toward notching the Gibb.
Although I'm glad it is on the tailstock side, it will be in the way of a future DRO Scale. That said, I'm still not happy with a scale in that area because I frequently bump my tailstock in there when I drill. This whole issue needs a lot more thought and maybe a novel dro scale solution of some kind. Perhaps up on top of the cross slide.
Although it looks REALLY COOL, I'm not real fond of the idea of a cam screw behind the scale. Way too probable that it will wear as time passes and need re-indexing just when you need it most. Murphy is not leaving town until long after my wife buries me and my junk out back.
Edit - I wrote the above over the course of 2 hours in little bursts while we picked up grandkids. So I didn't see the posts above until after I posted. I like
@RobinHood's solution. But my Gib lock screw is much lower (in line with the Gibb) and I don't want to put in a second screw. I'm not even sure there is room above the Gibb. So I still prefer to mill a small flat on my Gibb as described above.