The start of Hell's Challenger is different to what I do, but certainly acceptable - well done. I'm not sure if it's possible to block the part where you use the shimmier to stop the miner though. I may have to leave it. At least now you need to do release rate tricks to save a jumper!
To get the silver talisman requires some creative thinking though.
Steeplechase might require leaving as is.
ADDENDUM: There is one solution to fixing the last part of Hell's Challenger, but I fear that will damage the shape of the tank too much (it involves a 5th miner and a small break in the rear skirts, where any lemmings going leftwards will meet a fiery death in the middle of the tank, but a single lemming going right (the original miner) can become a miner and head to the exit. I'm in two minds about it... while it will fix the backroute and make hte use of the last shimmier a bit more innovative, I'm more concerned about the level's aesthetics. Plus you might still be able to use the shimmier to escape from the gap, or the jumper you saved. I might provide a side version later.