Just discovered a leak were the turbo bolts to engine. Peice of gasket missing. I'm blowing black smoke under load and have a loss of power. Also looks like a nut is missing from stud on right side. I...
Not a "must do", but just a suggestion. At the age of your engine, IME, it would be a good idea to replace the exhaust manifold/turbo studs, nuts, and gasket with factory OEM replacements, if possible/available. It looks from your photo that you have good access to the turbo.
Having a turbo exhaust leak puts additional stress on the remaining studs, as well as additional heat to the stud with the missing nut. You should be up and running in no time.