carb replacement suggestions

http://www.demoncarbs.com/Assets/docs/Products/Technical/LIT701rev10.pdf

This link is a copy of the instructions that I had and it says nothing about the adapter you are speaking of. The tech help people at Demon said nothing about it either.

Look at figure 7 of the link you posted.
It clearly shows the mopar throttle stud and gives you the part number.