I spoke to Bintel (I ordered most of the gear from there) and allegedly the Field Flattener adds 55mm to the optical path, so no additional bits are necessary. I can't think of a time when I wouldn't be using the flattener (perhaps I'm mad) but I guess we'll see if it all lines up as the rep from Bintel assures me it will.
**EDIT** Ahaa, I've just worked out I misread the query. I also ordered a
Canon Eos bayonet thingy to link the camera, but forgot to put it on the list.