Here is my dilemma. I have a never used European headlight unit (bucket and Cibie glass lenses) I bought 40 years ago for my '78 XJ-S project which was never completed. Now I am working on a '92 XJ-S convertible which I would love to install the never used Cibie glass lenses and replace the dull plastic lenses. Does anyone know if the older lenses will fit the newer Jag? My never used set is a complete un it i.e mounting bucket and glued in glass lenses. I could remove the lens but then it is no longer a “never used” unit which will probably depreciate the re-sale value. Looking at the earlier unit, it looks like the sealing flange is different from my '92 which would probably make the swap impossible. Does anyone know if these earlier lenses are compatible with my '92 and '92 chrome rings?
First off, do your Carello headlights have E-code markings or DOT markings? Or, to put it another way, do they use H4 bulbs or those 9000-series bulbs with the plastic base?
The reason I ask: If they are E-code, you should try to keep them! Or at least sell them to some other XJ-S owner. OTOH, if they are DOT, they are garbage, any scheme to replace them with something else is justified.
If they’re good units, several have reported that you can heat the entire Carello headlight up in an oven until the glue softens, then you can separate the lens from the reflector. That makes it easy to clean up the lens. The only issue is gluing it back together, but believe it or not there are products made specifically for the task. Or some have just used silicone sealant.
I’m pretty sure the Cibies can be used, but it’s probably fiddly. The Carellos have remote adjusters, dunno if you can use those. You might need to convert to the entire earlier headlight mount scheme.
BTW, which Cibies do you have? The earlier Cibies have a separate reflector for the main beam that has its own adjuster, and two H1 bulbs are used. Later Cibies have one large reflector and use a single H4 bulb.
Check out that white stuff that is used when gluing in replacement lenses for the front fog lights, similar to RTV, following the same process Palmdude mentioned. I forgot what it is called. It is on the “tips” section of either the Welsh Enterprises or SNG Bar. websites, under subheading “fog lights”. 
I don’t think the headlight bezels are interchangeable.
They will not fit into the headlight opening, as far as I recall.
Yes, the Carello lens has a “DOT” code and made in UK. It was very easy to separate the plastic Carello lens from the bucket since there were clips and a little glue holding them on. But my first option which I would like to pursue is to use the glass brand new ('78) Cibie units with the original '92 buckets. My Cibie units utilize 2 bulbs and it is noted for LHD made in France E2 HGR. I have successfully used the oven procedure when replacing the fog light lens and plan to do the same thing with the headlight unit to separate the glass lens.
Bummer. Could I check that by just test fitting my '92 chrome ring over the Cibie?
You could. That’s how I found out.