Replacing my sunroof (XJ6 X300) with a used 200? Xj8 assembly. Why glass rather than the steel in my original? Glass is heavier, considerably more prone to breakage and, with the sliding panel ever present affords no aesthetic advantage. I am simply curious.

Heads up on something the man at the salvage yard pointed out was that there was a difference between the X300 and X308 setup and SWB vs. LWB

I don't know if it is true or not as they have a X300 to pull some sunroof parts for me and using that one .

SOunds to me like you've got your hands on the sunroof glass from the X350/358 series. If so, I reckon the added weight and fragility will be the least of your issues. As far as I know, X308 was not offered with a glass panel.
While I suppose it's possible that (X358 panel) may transfer to an X300, IMHO it would be more likely to fit an S-Type.

Parker, sounds like bad gouge to me - I *think* X308 and X300 sunroof bits are interchangeable across the range, even between LWB and SWB. Maybe Motorcarman will happen by and set it straight - I know he knows.

There is a X300 to get the unit from and there is a X358 that I can at the least get the panel measurement .

I too am not aware of any differences between X308 and X300. My car is built on an X308 body shell and the original donor X300 sunroof assembly fitted straight in with no drama (unlike some of the other bits).