Yes but this does not change the WHOLE "BY GRACE" through faith in God. Honestly the dynamic is no different, but the second half of your comment loses me completely. I do not understand where the disconnect here is. Yes they did not know about the ultimate plan to pay for the worlds sin, to pay for their sins. We agree on this point, but where I think we are parting company is that faith in the Fathers is at all different as faith in the Son. Faith in God is faith in God in my opinion, which in this context I know means very little, but I'm hoping you see why I think this way.If you read Hebrews 11 literally, they were saved by putting their faith in what God told them to do. Their faith involves a work of some kind.
For example, Abel offered the correct sacrifice Hebrews 11:4, Cain didn't want to even after God gave Cain a second chance by reminding him to do what Abel did. (Genesis 4:7). Note that it was about doing for both of them.
Abel was saved by that faith, shown by his work.
THAT is what I am saying. God never told Abel and Cain that his son will die for their sins and rise again on the 3rd day (aka 1 Cor 15:1-4)
Moses hadn't even received the law yet, of course they had no clue about Jesus, but by His grace, through faith in the "I AM", YHWH , they were saved by the blood of the King to come. I see no disconnect at all, it's all rock solid in my view. Way do you feel it's insufficient they believed in our God in the way He revealed Himself at that time to them. At least do you think this makes sense?