I'm not familiar with them GG64 but looking around the web it looks like they're light-weight, flexible crampons designed for general walking - no technical stuff. Sounds like they might be very similar to my Kahtoolas. The Kahtoolas fit on just about an boots and the makers claim you can even use them on approach shoes, though I reckon you'd get awfuly cold feet walking around in snow in approach shoes! Bear in mind that I'm making an assumption that they're like the Kahtoolas so don't take this as gospel...
Do they fit your boots? That's really the best test.
Pretty sure you have a pair of aluminium 'just in case' crampons. Good for ski-mountaineering and occasional use. Unless there is good snow cover, they will wear down quickly. Had a quick google and they seem to be C2 on some websites. There are a couple of camp xlc models though, so i would check further. One model has steel front points. I wouldn't buy a new pair of boots just to suit, if you got them cheap. They'll probably last you ages if you carry them in todays UK climate.
On the xlc's, folk are right that they were designed as a lightweight alloy item for ski-touring etc. where they're likely to be carried more than used. And being alloy they will wear down quite quickly in contact with rock.
As for the rating, I'm not certain but a couple of points should make it pretty clear....
i) Is the bar linking the front and rear sections flexible or rigid, and
ii) Have they got front and rear straps (the original design) or the rear step-in binding like the pictures on the various web retailers now?
If rigid bar and step-in rear binding then a C2 rating would sound about right for them to stay on securely (and bear in mind they were designed with ski boots as much as walking boots in mind). But if the bar is flexible and they have straps all-round then they'll be fine on a B1 boot and I'd say for basic snow walking rather than anything technical, with most B0 boots too (make sure the straps don't compress the uppers and squash your feet).
