Do you believe there is a difference between eternal life and credited righteousness?
Absolutely.
First, consider that Abraham was credited as being righteous through belief, yet Abraham died not having his sin atoned for. So we see the principle of credited righteousness outside of an eternal context.
Secondly, we know that the "True Bread" came down from Heaven for the express purpose of bestowing Eternal Life to men, the implication being that it was not taking place before:
John 6:32-33
King James Version (KJV)
32 Then Jesus said unto them, Verily, verily, I say unto you, Moses gave you not that bread from heaven; but
my Father giveth you the true bread from heaven.
33
For the bread of God is he which cometh down from heaven, and giveth life unto the world.
John 6:48-53
King James Version (KJV)
48
I am that bread of life.
49
Your fathers did eat manna in the wilderness, and are dead.
50
This is the bread which cometh down from heaven, that a man may eat thereof, and not die.
51 I am the living bread which came down from heaven:
if any man eat of this bread, he shall live for ever: and the bread that I will give is my flesh, which I will give for the life of the world.
52 The Jews therefore strove among themselves, saying, How can this man give us his flesh to eat?
53 Then Jesus said unto them, Verily, verily, I say unto you,
Except ye eat the flesh of the Son of man, and drink his blood, ye have no life in you.
We can pinpoint the time when the True Bread came from Heaven, that being the time of the Incarnation. Christ defines this "bread" as His flesh (v.51), which we understand to refer to the Cross, His death in the stead of the sinner. Those who received the physical sustenance of manna, which He contrasts His flesh (the True Bread) with are shown to be dead. In view is not physical life, but spiritual life.
And Christ makes it clear that except one eat of His flesh and drink of His blood (believe on His death), they have no life in them. All hearing this teaching would have had physical life, but, they, nor the "fathers," and this was have included Moses, do not have the Life which Christ came to give, which is eternal.
Righteousness, on the other hand, is the very reason why Christ had to die in the stead of the sinner. Abraham was credited as righteous, but that made him no less in need of salvation in Christ than any of us.
The way they are typically explained, it seems that eternal life is a current possession, but righteousness is not.
We stand, positionally, as being credited as "righteous." It is imputed righteousness just as it was for Abraham.
Romans 3:20-25
King James Version (KJV)
20 Therefore by the deeds of the law there shall no flesh be justified in his sight: for by the law is the knowledge of sin.
21
But now the righteousness of God without the law is manifested, being witnessed by the law and the prophets;
The Law could have given life if one had been able to keep it. Here we see that the Righteousness of God is, apart from the Law, now manifested.
The next verse shows imputation of that righteousness to the believer:
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:
23 For all have sinned, and come short of the glory of God;
24
Being justified freely by his grace through the redemption that is in Christ Jesus:
Abraham was imputed righteousness through something he did: he believed.
We are imputed righteousness through something Christ did: He died in our stead that the penalty for our sin might be eliminated, and that we might be brought into a position of justification, not because of something we did, but because of something Christ did.
This applies to the Old Testament Saints as well:
25 Whom God hath set forth to be a propitiation through faith in his blood,
to declare his righteousness for the remission of sins that are past, through the forbearance of God;
Now, if you mean righteousness in a context of ourselves living righteously, that too is something we have the potential for (though not in a context of sinless), because the Word of God has always been a cleansing agent, and we can rid ourselves of the sins that so easily beset. The blood of bulls and goats, and calves for that matter, could not take away sins. But, I believe the Writer of Hebrews meant to imply that salvation in Christ can take away both the penalty for sins, as well as sins in our daily conversation.
Do we actually have eternal life, or is it only credited?
We actually have Eternal Life based on the Eternal Indwelling of the One Who is Himself...Eternal.
Eternal Life is not a substance poured on the believer. It is not a positional standing of the believer. We are, when we are indwelt by God, resurrected spiritually from the death exampled in John 6 above. That is Regeneration, the New birth. We are new creatures because we are something that previously we were not, which are children of God who are in unity with God the Father, Son, and Holy Ghost:
John 14:20-23
King James Version (KJV)
20
At that day ye shall know that
I am in my Father, and ye in me, and I in you.
21 He that hath my commandments, and keepeth them, he it is that loveth me: and
he that loveth me shall be loved of my Father, and I will love him, and will manifest myself to him.
22 Judas saith unto him, not Iscariot, Lord, how is it that thou wilt manifest thyself unto us, and not unto the world?
23 Jesus answered and said unto him,
If a man love me, he will keep my words: and my Father will love him, and we will come unto him, and make our abode with him.
Do we actually have righteousness, or is it only credited?
In a temporal context, that is an ongoing debate, lol. Sometimes we are righteous, sometimes we are not. We cannot expect a sinless existence until our physical bodies undergo the same event our spirits have: resurrection. We await the redemption of our bodies, which still lay under the curse, and are still in a fallen condition. That doesn't mean we have no power not to sin, it just means we have no power to be sinless. Only Christ is.
God bless.