gearbox query guys

hi as u may know im trying to sort my g/box out im looking down the 2nd hand road i have found one i think?? my car is a 3.7 sport with a 5 speed auto zf box with the code 5hp-19. the box i found is out of a 2.6 twin turbo s6 with the same code 5hp-19 will this fit need to know asap guys as im about to part with half a grand thx