I know - I still shudder to think of them lugging a heavy chain up the side of Winnats behind Speedwell to stake out and sight the level bearing on the surface.
His description of the route down is spot-on though, at least until he gets to the streamway. Then it all seems to get a bit hazy and he's suddenly at the Bottomless Pit. I have to assume that the 'original' Assault Course passage end was already buried beneath the streamway floor when he visited, though it's unclear when that was exactly. Eede's Grove was the mine shaft he actually dropped, and I think that was bought by Oakden and co when they opened up the system, so it's certainly around 1780. But I suspect from his description that he went via the 'Trevor Ford' passage, rather than taking the tubes to the Whirlpool and then back down the streamway.
I went in with Nigel Ball a few years ago, and he dug out the very top of the Assault Course passage where it meets the streamway - wearing a facemask and a small cylinder. I had to stand on his back tp keep him underwater while he dug! But he did open it up a bit, though it was obviously pointless to go any further - it was just to prove the point really that it was
there under the backfill. I'm surprised Pilkington (or anyone else for that matter) never mentioned the Pit Props section, as it surely must have already been in work by then. The significance of a 40m branch to the canal being blasted (of equal proportions to the main canal), seems to have passed most historians by, especially when you think what's beyond it. Most of the ore came from there, for one thing. I remember coming out of there once with Wayne after a digging session and we bumped into some students coming from JH or Titan in the branch canal, and they thought it was the Bung connection. We told them it was next turn right, and they all trooped off. No-one asked where we'd been - they never do.
Also - Pit Top Passage, as the top of the Bottomless Pit, is the closest part to Pilkington's series, above the canal. The choke at the end is just waiting to be dropped, and it has flowstone amidst the deads. I have asked once about having a go, but it just got a chin-rub in response. There's really only one way to do it, and it would be quite loud. But it if it didn't work, it would still just be a choke.
If it did
work...there's plenty of stacking-space too