Bought these and fitted to the Coupe today as I wont be using 7" and 5.75" lamps for much longer. Same will be fitted on the KAD convertible.
I think they do they trick just nicely. £17.50 each from Revotec ......and the best thing is they fit directly in the cibie brackets so I can position the air flow too!
They are not on the site yet as they only came back form the supplier yesterday. http://www.revotec.com/. The 5.75" ones are the 89mm duck fitting.
...also if you want a more powerful heater you can use the ram effect by ducting up to the heater motor box. They've certainly drop my engine temps a few degrees.
As always, totally reversible to stock, although this is unlikely.
Cheers,
David