Hey Zonest,
I may be mistaken, but I believe Paul (Romans 4) is referring more to Abraham's faith that God would give him a son in his old age, and that he would raise up another son when God tested him to see if he would sacrifice Isaac. If Abraham's faith resulted in his making a choice to sacrifice Isaac, then the choice (if a work) could be seen as contributing to Abraham's righteousness, (salvation from the Law). Certainly that choice was based on faith, which would not be possible without grace, but is it still a choice? Could Abraham have refused?