You're right, there is one rail on each side. Not sure with the XF, but with the earlier vehicles, you had to drill out the floor pan (two holes each side) next to the tranny tunnel to fit buckets. The crush tubes should already be in the strengthening rail under the floor. May have to add some reinforcing under the floor where one of the bolts goes through from memory. Best to get this plate from under a bucket seat vehicle - just drill out the spot welds and re-weld it into yours.
As for using Honda seats, they will have to be attached to Ford rails. Quite often, an adapter frame may need to be made, which I guess would require an engineers certificate. And I don't think that's cheap!