I know I am a bit fussy about preambles, but when instructions are complex I think setters should take especial care to ensure that they accurately describe what has to be done. Here we have two grids, and it's natural to assume that the 'first grid' is the one on the left, the second the one on the right. What the preamble should have said is something like this: "Another part of the hint says what solvers must do to the positions of the letters in each grid to supplement the second grid; this will enable solvers to complete both grids unambiguously."
As it stands the preamble is not accurate.
I imagine I'm the last to finish the puzzle. Not all mental slowness on my part - I've been tackling the puzzle in short bursts in between dong other things. However, if anyone is still solving the puzzle, it helps to have the list of integers in numerical order from the start. As one assigns the letters one can see words forming, which can help to narrow down the choices for some letters.