Perhaps I'm slow, but it hit me overnite that other than bunkering (which is minimal, as discussed) , there is really very little work that would need to be done to restore the old routing/holes.
The first five holes are essentially the same, then you would need to clear the hillside of trees for 6, which would also expose the old 12th tee.
Then, 7, 8 would be the same and for 9 all you'd need is to clear the row of pines planted to separate the re-routed fairways.
Then, for 10 you'd need to clear a few pines to play to today's 14 green, and then you could take out the entire row between today's 14 & 15 to expose the old 11th fully.
12, as discussed, and then you come to the biggest part of the project, the reclamation of the driving range for golf and finding/establishing the old 13th tee and fairway. This could be easy or hard depending on the amount of desired earth-moving to recreate former topographics but all in all still not earthshattering.
If there was a desire to recreate the original par three 14th across the creek, this might take some doing, given the proximity of the creek to the green and possible environmental issues.
After that, reestablishing the old back tee on today's 9th hole and that should be it!
So, I really see it in two major sections;
1) Clearing the old 6th fairway of trees.
2) Reestablishing golf on the driving range holes.
The rest if just removing planted fairway-separating pines, and building tees.
Of course, that's not the whole project...there's also irrigation, rebuilding a few greens, rebuilding tees, rebuilding bunkers, but strictly from a routing perspective, I think that's it.
Am I missing anything?