Check out Moss Motors . Their TD site shows all the parts that make up the folding windshield but if I am seeing the page correctly , some of the parts are no longer available. Occasionally one shows up on the web used, but if you can find one ,the cowel must be reshaped removing the flat shaped area that the Duchess windshield frame bolts to.
Check Ringo’s Duchess in the photo gallery. His car has the Duchess frame with special covers attached to the frame and cowel. It does not fold down but does look more like the original MG.
The top attaches to the windshield differently ,a bow ,usually made of wood , with the top material wrapped arround it attaches the top to the windshield frame.
Awhile back, a forum member actually made this modification. I think you can find it in Deerebill’s gallery