Quaife shelled gearbox quandary.

I'm in a position to have two projects one the go at the moment, they both have quaife shelled 4 speed gearboxes does anybody know if the standard rear engine/gearbox plates need adapting to accept these modified boxes? I have a '74 850 that I replaced the plates due to corrosion, the gearbox that I removed now doesn't fit? neither does the Mick Hemmings built gearbox I have from a 750. They are very different gearboxes looks wise but neither fits? I'm feeling a bit stupid at the moment?