I set this up a few years ago, and did once before and plan someday again to do day 3.
Now I sadly don’t have Civil War miniatures, but play it out with Napoleonic era troops, Prussians as the North, Russians as the Confederates. I use the exact OOB of Gettysburg transferring to made up units. I spent a lot of time replicating the battlefield from the map made a year after the battle. I do think many miss the amount of fencing and stone walls, I had a time making more fences to get what I think is called for.
The Russians did get a hold of Devils Den but couldn’t hold it, the attack otherwise went pretty much the same as Day 2 went. I do want to do Day 3 someday, the Russians do have enough Position batteries to reach Seminary Ridge.