14105603 is the only part number that I can find still available ($45.71 + S/H).
Its description says that it is for the MG2 and M17 transmissions (I think that's getrag and muncie 4spd.)
But, it also says that it is for the 2nd design master cylinder, with the pipe fitting in front of the fluid tank. This info is coming from a 84-86 22P book.
Since Black86SE is putting a isuzu 5 speed into his car, and I think he already has a 2nd design master cylinder, can someone with a 84-88 22P book look up and see what the number is for the line that would fit a 87 Fiero with 2.5L engine and isuzu 5 speed trans?