I've noticed the general rule when installing an s14/j30/q45 diff into an s13 is to get solid diff bushings. My concern is that the top bushing is dropping the nose of the diff by 1/4" or more. My reasoning is that the metal 'ears' on both s13 and s14 are cast at the same level. Now this is of no concern if the s14 ears are cast lower, making the spacer necessary. This also is of no concern if installing in an s14 or even leaving rubber bushings as these would conform to misalignment.
This could cause a bending moment on the rear bolts/cover since the diff isn't sitting parallel. It would also create a slight driveshaft misalignment (generally not an issue as this joints are made to cope with it.
Does anyone know if s13/s14 ears are cast at the same level? I'll be installing an s14 diff soon and am wondering if I should be cutting my solid bushings flush w/top surface.
thanks