Finally I have all the extra letters and see what thematic treatment is required. I have 4 such words.
6 A is proving difficult.
Flash and Shock enveloping both ends of large megaphone (6)
Flash has two letters? Cannot find a word for shock. Assume megaphone is the def.
Also is 45a Mushroom cocktail (4) with thematic word become (5,4)?
I still have to work on 37A and D, 38D.
Thanks for help.