These days, so many PO's (prev. owners) swap so many components/parts, it can be a struggle
to match things up.
As you see in Seabroncs diagram, the ****** (in some cases called a yoke) needs to match the CV bolt holes.
You can measure the bolt holes on the ****** & CV attach point so as to obtain correct fitment.
If the differental end doesn't match, measure as well.
Should the answer be to change both the ****** & rear yoke..., the large nuts that hold them on are
special locking nuts that come off & on fairly tight. If loose.., they need replacing.
Also need proper torque.
I'm not fimilar with the FSB's Someone with a '90 could measure theirs as well so you could know
where you stand. Could be the driveshaft you have is for a different year.. <_<