Went through this last year when installing an overhauled engine in my BJ8. The new mounts--side and top--I got from Moss were, well, not the best of quality. I've noticed the newer ones tend to sag and if they sag too much the rubber will begin to tear off the metal backing plate (which happened on our BN2 when we installed the engine years ago). When I installed the engine in the BJ8 it appeared to me the gap between the top mounts was excessive--a quarter-inch or more--which would allow the side mounts to sag quite a bit (then tear?). So, I 'ballparked' a measurement, cut slots in some fender washers to clear the stud and stacked them up to close the gap between the top and bottom mounts. Not an elegant solution, but at least it should prevent the side mounts from sagging and disassembling themselves.
We kept the OEM (AFAIK) mounts from the BN2; there is definitely some difference in quality between the originals and what I've seen in the aftermarket. I may end up putting them back in someday.