Try Richard Isenberg at Southend 01702 547 490 . I have only heard good things about him and I am very pleased with the work he did for me. Very knowledgeable, very helpful. a real craftsman. I would 100% trust one of his engines. I doubt he would bodge anything even if you asked him to.
Give him a call and discuss what you need doing. His advice will be invaluable even if you go elsewhere, however, I bet you'll take it to him after speaking with him.
DJ