Hi Jon,
Yes that's is how I envisaged you doing it.
Obviously, if you can mount them on the face plate and they swing clear of the bed (in the gap) then that would be a better solution since you would be able to tackle the entire width and lengths of the outer faces with the lathe tool for less cross slide travel.
You would then only need to use the mill for taking the radius-ed edges down square to generate the initial datum faces, for squaring off the ends and to cut any required slots (use a slot drill, not an end mill for these) after the main faces are finished.
You could do the same using the mill, if you make up a fly cutter... only issue this would bring will be the need for even more travel to go end to end and clear the cutter although this would only be the case for the larger unit... the smaller one will not have this issue.
The face plate solution is the best option for the large outer faces and will also result in a cleaner surface finish... end mills always leave tram lines on wide faces.
I am sure you will make a god job of them, just take your time and dial in carefully where necessary.
Good luck and stay happy.
Sandy.