Jim, Try this or something like it. It's what you photo reminded me of.
Ball Joint, Mono-Ball, Full Size, Right - Racing Parts and Products
I used these on several Yenko Corvairs in years long past and assisted with another non-Alfa application. You should be able to source a threaded rod with a flat to bolt or weld this plate to, and then a clevis rod to form the back of the a-arm.
At the risk of stating the obvioius don't attach the sway bar link to the clevis arm as it's not meant to take a down load like that.
Additionally the heim bearing is a nylon type so welding edge of bracket instead of bolting must be done with tig and little at a time to keep from ruining the bearing liner. Bolt if you can.
Also I have seen the supplied ball joint taper pin crack and break. For this reason I always drill/ream the ball joint mount on the spindle all the way through and then use a NAS shear bolt retained with threaded nyloc nut and cotter pin.