Lloyd & Steven,
Regarding possible slight differences between M8 and M9 baseplate size...this issue seems to have only come up recently, ever since RRS designed their new Base/grip/QR plate for the M9 and initial ones were too tight. Prior to that I and most everyone else assumed the there was no size difference. I have a M8 grip which I use as Steve wants to use,...that is to attach a QR plate to the Leica gip bottom to have ready when a tripod is used. I've tried it on two different M9 bodies and it fit perfectly and about the same on both. What's interesting though is the original non-grip baseplate on one M9 attached with the same amount of tightness as all M8 and M8.2 baseplates I've tried.....but the slightly later M9 original baseplate seems fits much tighter. Whether this is by a design change by Leica of not, I can't say...but the M8 grip did fit on both these M9's without an issue. I cannot say if this is universal, but thats been my experience so far.
Dave (D&A)