Fins or no fins on the bottom of the case?
OD came in different varities depending upon year. For an E9, the one you have pictured would not be a first choice.( If indeed it is a 5 speed)
Seperate or integral bell housing- your picture says integral. Two choices.
Fins- fins are good. They indicate of the latter choices, a more robust choice:
260/5 - 2 piece aluminum case with integral bell housing ---- No fins - No Intermediate section, was used in the '83 - '84 cars,
265/6 - 3 piece aluminum case with removable bell housing - No fins - 97mm Intermediate section, - used again only in '85
260/6 - 2 piece aluminum case with integral bell housing ---- With fins - No Intermediate section, was used in '86 and on
280/5 - 3 piece aluminum case with integral bell housing ---- With fins - Small Intermediate section, was for the ///M cars
The three piece case 265 with seperate bellhousing w/ mechanical tach is the preferred choice if you're hunting.