Please forgive the volume of this post. Skip to the bottom for the summary if you like.
The issue, as I see it (which is perhaps different than what the OP was thinking), is an apparent contradiction between the phrases, "faith of Christ" and "faith in Christ". The KJV uses "faith of Christ" or close variants in several places, and at least one KJV-only advocate argues that it is Christ's faith that justifies us, according to Galatians 2:16.
Romans 3:3 For what if some did not believe? shall their unbelief make the
faith of God without effect? (NASB: faithfulness)
Romans 3:22 Even the righteousness of God which is by
faith of Jesus Christ unto all and upon all them that believe: for there is no difference: (NASB: faith in)
Galatians 2:16 Knowing that a man is not justified by the works of the law, but by
the faith of Jesus Christ, even we have believed in Jesus Christ, that we might be justified by
the faith of Christ, and not by the works of the law: for by the works of the law shall no flesh be justified. (NASB: faith in for both)
Galatians 2:20 I am crucified with Christ: nevertheless I live; yet not I, but Christ liveth in me: and the life which I now live in the flesh I live by
the faith of the Son of God, who loved me, and gave himself for me. (NASB: faith in)
Galatians 3:22 But the scripture hath concluded all under sin, that the promise by
faith of Jesus Christ might be given to them that believe. (NASB: faith in)
Ephesians 3:12 In whom we have boldness and access with confidence by
the faith of him. (NASB: faith in)
Philippians 3:9 And be found in him, not having mine own righteousness, which is of the law, but that which is through
the faith of Christ, the righteousness which is of God by faith: (NASB: faith in)
James 2:1 My brethren, have not
the faith of our Lord Jesus Christ, the Lord of glory, with respect of persons. (NASB:
your faith in)
Revelation 14:12 Here is the patience of the saints: here are they that keep the commandments of God, and
the faith of Jesus. (NASB:
their faith in)
However, it also talks about the faith of people:
Romans 4:12 And the father of circumcision to them who are not of the circumcision only, but who also walk in the steps of that
faith of our father Abraham, which he had being yet uncircumcised. (NASB: the faith of)
Romans 4:16 Therefore it is of faith, that it might be by grace; to the end the promise might be sure to all the seed; not to that only which is of the law, but to that also which is of
the faith of Abraham; who is the father of us all, (NASB: the faith of)
2 Timothy 2:18 Who concerning the truth have erred, saying that the resurrection is past already; and overthrow
the faith of some. (NASB: the faith of)
Titus 1:1 Paul, a servant of God, and an apostle of Jesus Christ, according to
the faith of God's elect, and the acknowledging of the truth which is after godliness; (NASB: the faith of)
Revelation 13:10 He that leadeth into captivity shall go into captivity: he that killeth with the sword must be killed with the sword. Here is the patience and
the faith of the saints. (NASB: the faith of).
Other than in cases using the singular-specific "thy", there is no disagreement between NASB and KJV in the 35 places that Scripture uses the phrase, "your faith", meaning the faith of people. Not a single one attributes the
locus of faith to Christ or God, though He is the
object of faith in every case.
Returning to the verses where the NASB differs from the KJV, not a single one has a textual variant. That means that the difference is entirely one of interpretation; how the KJV translators used "of" and how it is used today. Because the locus of faith is
always in the believer(s) where they are being addressed directly, it is reasonable to conclude that the locus of faith is also in the believer in the "faith of" verses. In other words, "faith of" is a 16th century way of saying "faith in". It isn't the faith "located in Jesus" that justifies us, according to Galatians 2:16, but the faith located in us. God/Christ is the object of faith, not the "exerciser" of it.