I have now fitted clear rear lenses as per Paul's photo - but sourced from Ebay for £9 the pair. They are Lucas L691, and the clear lenses do look good on a silver Morgan.
The only slight hassle was getting the orange bulbs, as they are "inline pin" which are usually clear, whereas most orange glass indicator bulbs are "offset pin" - watch out for this, as they look the same but are not interchangeable.
