that picture is a Tubus Duo a bolt runs through the fork blade , and the rask is strut braced on both sides .
so step 1 is a new fork without suspension to make that work ..
well seems a modest adapting a standard Tubus style and adding mounting clamps ..
but cleanly done..
My Koga Miyata WTR had a particular Spinner fork re machined
WB Bicycle Gallery: Robert Clark's Koga Miyata WTR
top rear is a special block [Plain finish AL] there is a raised boss in the slider casting to screw into.
the block offers a place for the top rail to bolt to, at right angles to that.
+ the tip of the fork is drilled and threaded, for the bottom mount ..
painted to match etc..
machine shop access is a wonderful thing ..
one problem the Tubus swing solves was by not adding to the unsprung weight
the suspension was more active but unfortunately as the mount was around the fork crown
(+ braced to the steerer above the headset on top)
and there are a whole lot of fork crown shapes out there
getting it to be adaptable to any fork really was not possible
think they are discintinuing it
the trade show sae a reverse fork where the plunger was in the bottom
and the legs had the mech and crown in the same piece
they were not thinking of luggage on that either ..
removing the suspension fork may be best, simple and reliable minimum weight and moving parts ..