Here's why the 1st Resurrection CANNOT be equated with the resurrection of just persons at Christ's Crucifixion:

Let's look at the actual Text
.
Matthew 27:50-53
50 Jesus, when he had cried again with a loud voice, yielded up the ghost.
51 And, behold, the veil of the temple was rent in twain from the top to the bottom; and the earth did quake, and the rocks rent;
52 And the graves were opened; and many bodies of the saints which slept arose,
53 And came out of the graves after his resurrection, and went into the holy city, and appeared unto many.
And let's look at the only passage of Text that actually contains the words "First Resurrection," (Greek has it "The Resurrection the First).

Revelation 20:4-7
I saw the souls of them that were beheaded for the witness of Jesus, and for the word of God, and which had not worshipped the beast, neither his image, neither had received his mark upon their foreheads, or in their hands; and they lived and reigned with Christ a thousand years.
5 But the rest of the dead lived not again until the thousand years were finished. This is the first resurrection .
6 Blessed and holy is he that hath part in the first resurrection : on such the second death hath no power, but they shall be priests of God and of Christ, and shall reign with him a thousand years.
7 And when the thousand years are expired, Satan shall be loosed out of his prison,


Observations:

1) It is understood that Revelation's visions were given AFTER the Cross, AFTER the "many bodies of the saints which slept arose" thereat. Therefore, Rev. 20:6's exhortation to faithfulness during the impending adversity, "Blessed and holy is he that hath part in the first resurrection" would be inane - merely informing those first readers of Revelation that those folk who came back to life decades previously at the Cross were "blessed and holy." Lazarus also had come back to life just a week or so before; as had the widow's son at Nain (Luke 7:15) and the synagogue ruler's daughter (Mark 5:35-43) had earlier in Jesus' ministry; a boy came back to life when Elisha layed upon him (2 Kings 4:32-35); a man came back to life upon falling upon Elisha's bones (2 Kings 13:21); Moses appeared very much alive on the Mt. of Transfiguration (Mat 17:1-4) centuries after his death recorded centuries before (Deut 34:5). None of these were the First Resurrection of Rev 20.

2) Rev 20:4 actually describes those who rewarded by the First Resurrection as "the souls of them that were beheaded for the witness of Jesus, and for the word of God, and which had not worshipped the beast, neither his image, neither had received his mark upon their foreheads, or in their hands" -an overt reference to the very Tribulation the Revelation was given as encouragement to overcome. This Tribulation came many years AFTER THE CROSS. Again, these cannot be the same folk who were resurrected at the Cross several decades before the beheadings, Beast worship, Beast-image worship, Beast-mark receiving, etc, began.

3) Rev 20:6 speaks in future tense -future to the giving of the Revelation- of those resurrected in this First Resurrection: "They shall be priests ... " and "[they] shall reign with Him a 1,000 years..."

4) Rev 20:7 "When the 1,000 years are expired, Satan shall be loosed..." Those who insist that the First Resurrection takes place with those resurrected at the Cross circa 30ad, and then go on to assert that "1,000 years" really means "40 years," must also say that Satan is loosed when Jesus comes back at the end of the make-believe "1,000 years" in 70ad: Entirely at variance with the conclusion of Preterism's message, The 70ad Victory of Christ.

Other words could be rightly employed here, but let it suffice to say that it is entirely untenable to posture that those raised at the Cross represent Revelation's First Resurrection. Preterist Christians can do better than this, the very hermeneutics that deduce the Preterist perspective demand it.
*Feel FREE to claim as your own anything I write - while I retain the right to do the same with it*