If all else fails, you can make a bespoke one to clamp the FTI to the stem on your your Mag Base column
After all, we are supposed to be Engineers, with the ability and facilities to make things!
(Two small pieces of square bar, each with two drillings (Reamed holes would be best ) at right angles to each other. On one piece sized to suit the column on the Mag Base, and to suit the DTI stem on the other, with a common sized drilling, to suit the clamp screw.
The only other operation is to slit each block across the clamp screw drilling, so that tightening the clamp screw closes the slit.
If you cannot make a knurled knob for clamping, an Allen capscrew and nut will do the job.
It may be a hybrid, clamping to a metric column, to hold an Imperial stem DTI.
"C'est brusque, mais ca marche"
SO WHAT?
It will do the job that you require.
Or if the hole in one part matches the Mag Base column and the other is oversize for the DTI stem, turn up a sleeve to match the stem to the hole, and split it.longitudinally.
Howard
Edited By Howard Lewis on 23/06/2021 15:12:31