Would be nice to get to know your camera lens combination. May be you can swap MFR170 from Upper Rail Use to Lower Rail Use and use MFR210 as upper rail. Depends on your lower rail setting.
Just checked the NN e-store for you and there is no limitation of delivery of M1-Nadir Adaptor. They are in stock. Because you have an emergency case, just contact Bill on monday and I am sure he will help you.
Anyway, would be good to get the camera lens combination you use to check it with Nadir Adapter on vertical rail. I know it is late in EU, but I hope you check the forum this evening.