three suspension questions
FWIW, that's basically the exact part you can buy pre-made from bergman auto craft.
I believe Rick Ehrenberg once made an article about welding a simple splined collar to an existing steeringcoupler for use with the Borgenson box.
The cheap splined collar also came from Borgenson I recall.
I did this mod on my car, nice a simple with no drama :)
FWIW, that's basically the exact part you can buy pre-made from bergman auto craft.