no, do not put a crown over a mercury filling. if he is putting a crown over mercury, run and don't look back.
if your tooth is hurting that much and he puts on a crown and it is abcessed or becomes abcessed, you will have lost that money. what does he say is causing the pain? i would go get another opinion and see if the tooth is abcessed. it is difficult, because some dentists want to make money and will crown a tooth when it shouldn't be. i don't know about your case, but it doesn't sound good. did he use medicated cement to see if the tooth will calm down with a temporary crown?
about the epinephrine, he is lying or he is very stupid. my dentist has always used non-epinephrine, non vaso-constrictor for many years and most good biologic dentists do. no one ever bleeds to death, lol. that dr is nuts, run! the real truth is he doesn't like working with blood because he can do a cleaner job and see what he doing better. it is all about him. you are correct about the epinephine not being good and some people cannot have it. here is also the real truth, dentists keep on hand (or are supposed to) non-epinephrine anesthetic. people with neurological diseases are often told they cannot have it. when i had MS, it was one of the first things my dr told me. BUT, beware...because i asked for it one time the dentist (back home yrs ago) ignored my files that had big red letters on it and ignored me telling him i couldn't have it. i started to buzz and feel sick and half my body went numb. he said, oh i forgot, when i told him he gave me epinephrine! he didn't care.
the other thing that causes a cavitation is not pulling out the periodontal ligament, so if you are that concerned, see a biologic dentist who will do that.