Rhodedendrons will certainly do better in acid soils and most clay soils are alkaline therefore you are probably best just using ericaceous compost. They grow naturally (as I understand) in woodland so - dappled shade is best. The next best alternative I would suggest is somewhere which is not in full sun all day, but does get some sun for part of the day.

Wow Rogerbee,
That was quick, thank you.

I watched the sun most of today, a good excuse to be really lazy.
As we have a north facing garden it's always difficult, but now I know the best spot.
Love the Avatar, we have a Huge bumble bees in our garden this year,one has taken resident in a spare nesting box.
I knew i should have made that bumblebee box earlier.