An interesting point you make. Does that mean you believe some of what Paul taught to the Gentiles?
Do you believe all dispensationalists that separate themselves from Israel religious rites, laws, and ordinances to be hyper-dispensationalist, or just some?
Grace has always been, and you are saying God has always dispensed His Grace the same from the beginning. I really believe you have missed something. In His eyes, God only found Grace in one man, and surely there were many, many thousands, and most likely millions at that time. If justification has always been the same, then had some of us not get busy building a boat? I personally cannot start at this time for He has not told me to do so.
God in His Grace didn't do the WORK, but Noah had to do it. And what many dispensationalists believe is that Noah knew nothing about his salvation having to do by coming through the blood of God, our Lord Jesus Christ. The secret of all ages (dispensations) is to believe God, and what He tells you as you live, and not what He tells someone else.
The elements of the gospel have been know and taught by God from the beginning.
The works of man's hands (fig leaves) cannot be used as a covering for sin and death.
God Himself must provide the sacrifice/covering and that by the shedding of blood.
Genesis 3:21 Unto Adam also and to his wife did the LORD God make coats of skins, and clothed them.
A Deliverer/Savior would come from the "seed" (virgin birth) of Eve's progeny who would destroy the serpent and his works.
NKJV Genesis 3:15 And I will put enmity between you and the woman, And between your seed and her Seed; He shall bruise your head, And you shall bruise His heel."
All those who believed, longed for and looked for this Savior were saved by grace through faith in God's promise of a Messiah/deliverer/redeemer of believing mankind.
Genesis 22:8 And Abraham said, My son, God will provide himself a lamb for a burnt offering: so they went both of them together.
Genesis 49
10 The sceptre shall not depart from Judah, nor a lawgiver from between his feet, until Shiloh come; and unto him shall the gathering of the people be.
11 Binding his foal unto the vine, and his ass's colt unto the choice vine; he washed his garments in wine, and his clothes in the blood of grapes:
12 His eyes shall be red with wine, and his teeth white with milk.
Job 19:23
25 For I know that my redeemer liveth, and that he shall stand at the latter day upon the earth:
26 And though after my skin worms destroy this body, yet in my flesh shall I see God:
27 Whom I shall see for myself, and mine eyes shall behold, and not another; though my reins be consumed within me.
Isaiah 53
...
8 He was taken from prison and from judgment: and who shall declare his generation? for he was cut off out of the land of the living: for the transgression of my people was he stricken.
9 And he made his grave with the wicked, and with the rich in his death; because he had done no violence, neither was any deceit in his mouth.
10 Yet it pleased the LORD to bruise him; he hath put him to grief: when thou shalt make his soul an offering for sin, he shall see his seed, he shall prolong his days, and the pleasure of the LORD shall prosper in his hand.
11 He shall see of the travail of his soul, and shall be satisfied: by his knowledge shall my righteous servant justify many; for he shall bear their iniquities.
12 Therefore will I divide him a portion with the great, and he shall divide the spoil with the strong; because he hath poured out his soul unto death: and he was numbered with the transgressors; and he bare the sin of many, and made intercession for the transgressors.
And many others.
HankD