It isn't correct to say that the manual transmissions are exactly the same across the entire line, because they don't in all cases. With that said, the 318 and 325 do use the same transmission, so you should be fine on that level. You should be able to swap your old linkage onto the donor transmission. There are no differences in the trans tunnel or anything along those lines either.
1998 BMW 328is
1966 Pontiac GTO
2007 Subaru Impreza 2.5i 5-door
View my photos: Caught in the Wild