Take a small sledge hammer (2-3 lb) and start smacking the hell out of the arm. There are 3 cone washers below the nuts that keep the steering arm in place. You must smack the arm around enought to get the washers to unseat themselves and pull them out.
It can be a huge pain in the ass to do if there is alot of rust on there. Just starts swinging on the arm like you want it to die a horrible death and hope for the best. Hit the arm from both sides to help try and break it all free.
The best places to hit were the GM part number is cast into it and where the draglink end hole is at.
If none of this works get a bigger hammer.
Harley