The HUD does have the special windshield, but many people opt not to replace it if they can't afford it. It'll just ghost the image since the image would reflect off both planes of the glass, not just one like the HUD specific one.
As for using a C6 one, probably not as the shape is different most likely. I have a 98 GP, 93, 95, 97 and soon 94 and 96 HUD'* here and the bonnevilles are all smaller than the GP. I'm sure you could make it work with time and a dremel, but that'* not something I would do.
As for how it works, I was reading the manual on the GP one and it uses the indicators off the PCM. I think it is 4000 pulses/miles from the VSS line for the 98 GP. The bonneville should work the same way so you'd just have to check the numbers and wire it up.
2007 Saturn Aura XR | 1970 Chevy Blazer 4x4 | 1970 GMC 3/4 Suburban 4x4