The only thing I can think of that is that loud is bad motor mounts, but you say you changed them. Are you using the stock motor mounts from the new motor? I'd suspect a slight binding there or at the tranny mount with metal to metal contact.

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.