You said it came out all black but you didn't specify whether the emulsion side was black or the backing was black. If the undeveloped film has a medium gray emulsion and a shiny black backing that sands off easily with fine sandpaper, you're probably dealing with Kodachrome. If so, it can be developed as a negative in D-76. Do a trial run at 15 minutes on a snippet and stop/fix as you would any other BW film, then soak in a 10% solution of borax and scrub the black anti-halation backing off with a sponge. It could come out very dense and muddy, in which case you could bleach it.