The drop down notch is fine in a pinch for the MKIV, as long as you won't need it for panoramas, which you wont if you're bringing your 5DII also.

I agree with Jonathan that you don't need two L-Plates. The 5DII is FF and better for landscapes, so just get one custom L-plate. If you think you may eventually get a 1DX, then I would rather see you get an L-plate for that later on, as opposed to get one for the MKIV now.